One of the biggest reasons for the game being set a number of years after Fallout 3 is project purity. The water in the Commonwealth seems much 'cleaner' than it did in Fallout 3, and so it's very likely that the tech was brought further up the East Coast to New York and then the Commonwealth itself. This would put the start of the game after NV to allow enough time for this to be fully implemented. And so 2283 or 2285 would actually seem very likely.

A few far more straightforward reasons for a 2285 start date would be:

1. Progression of existing factions, including the remaining Enclave and CWBoS, to allow for any necessary 'changes' which may be featured in Fallout 4's story.
2. Arthur Maxson reaching the age of 18, and therefore becoming a viable player on the battlefield.
3. Other children from Fallout 3 featuring as advlts, including residents of Little Lamplight.
4. Project Purity being expanded along the East Coast to New York, and then the Commonwealth (as suggested by the clean water seen in concept art).
5. Dr. Li becoming fully established within the scientific community of the Commonwealth, possibly connected to the expansion of Project Purity.
6. Dr. Zimmer returning to the Institute (canon) and assisting with their Synth programme, which would likely have taken several years.
7. The overall 'progressive feel' that we see in-game including extensive rebuilding, that would certainly suggest a later start date.
8. Allowing for future titles to integrate elements from both East and West coast without breaking the timeline.

Individually, some of the above may not seem particularly 'strong', but collectively they do make my suggested start date seem a lot more viable.

Zimmer basically mocks the idea of purifying water in Fallout 3. I doubt radioactive water is a problem for them just by the nature of the fact Boston was hit by less nukes, much like how the water was fine in the Mojave due to House shooting down most of the nukes.

Following extensive research, I have found evidence of there being three nukes that hit in or around the Boston area: the first in Lincoln, the second in Prospect Hill, and the third in Boston Harbor (see http://www.gamesas.com/topic/1526246-the-glowing-sea thread for full details). This last nuke is critically important, as not only would it have completely irradiated the area of the harbor, but it would also appear to have led to the formation of the Glowing Sea, as I have detailed in the linked thread. For the record, I believe that if the Institute had a similar defence system to that used by House, then these three nukes are simply the ones that 'slipped through the net'.

Now, we know that Madison Li was due to make her way to the Commonwealth, and so a specific clean-up operation in Boston Harbor may well have been high on her agenda. Also, the comments of Dr Zimmer regarding project purity may even suggest that Harkness knew of certain 'classified' information, including the true origins of the Glowing Sea, which would give Zimmer even more incentive to 'recover' him in order to conceal such information. Note that once the water in the harbor is purified, there would still be a perpetual source capable of producing the radiation storms as mentioned by Todd in his interview immediately after E3. There would also be an added incentive for the Institute to protect the true nature of the location, as the existence of live reactor cores would prove to be an invaluable resource.

As an additional note regarding points 1 and 2 in my above post (CWBoS/Arthur Maxson), details are provided in https://www.youtube.com/watch?v=Sn0UuTSE5XM video that strongly suggest CWBoS as being behind the airship, specifically due to the Lyons insignia on the airship itself. This would further strengthen the suggested timeline as being accurate, and so 2285 is now a perfectly realistic start date. Note that in the video, it is also suggested that Maxson may well have moved to a position of power due to his legacy, which would fit with him being 18 years of age. Also, if the above information is correct, there would be even more reason for Todd and Pete to stick to their story of "200 years" so as not to give away vital plot details before release.

EDIT: the Lyons insignia is also on the power armor as well as the cloak pin seen in concept art as detailed in http://www.gamesas.com/topic/1524192-more-clues-in-the-concept-art thread, further suggesting Maxson's direct involvement and a 2285 start date.

Dr Li and Zimmer are good points but the big one to me is Arthur being 18. That is the reason I believe you could be right. I suppose he doesn't have to be 18 but it make sense. Also the point on how nice it looks is a big one. They have A LOT of electricity and sprawling towns. Though I suppose this could just be better tech for gamesas. Kinda like Star Wars 1 to 4

This whole Maxson thing doesn't make any sense. What is significant with him becoming 18 and becoming a major player on the battlefield? How? He would barely be an initiate with very little to his name outside of being a Maxson. He's "heir" to a lineage that harbored a belief in a dying institution back West. Him becoming 18 won't suddenly result in anything major happening.

The Brotherhood already had a major schism that is decidedly water under the bridge at this point, so Arthur suddenly rallying another legion of Brotherhood members to break off and follow him on an exodus to Boston is not going to happen. Additionally, he's under the tutelage of an Elder who feels differently about the Brotherhood's purpose and duty in the world. He's also heavily influenced by notable members like Sarah Lyons, whom he idolizes.

Here are some spark notes of why it's not the CWBoS in Boston (I won't mention the date being one of them because I'm tired of bringing it up):

->The only BoS group that used a fleet of airships was the MWBoS before they splintered off, and most of those crashed with one of the wrecks being located in or around Chicago (correct me if I'm wrong). They are the only ones in any position of rebuilding an airship and actually making an exodus further East.

->Elder Lyons' group walked all the way from Lost Hills over to the East, so airship tech is unavailable to them. Building one from scratch? Nope, they were pretty focused on rebuilding the walking, Anti-Communist Death Machine after it got canned.

->They wouldn't use an airship to begin with, especially after raiding the Adams AFB vertibird depot (and also the fact that they're like ~8 hours due south of Boston. Considering that they walked all the way across the North American continent, I highly doubt they'll be like "lets build us an airship to save us time in our travel to Boston up north."

->The Outcasts are still causing problems for the CWBoS in the CW.

Lastly, what elements from the West would hold any value over in the East?

Edit: I striked out the "water under the bridge" bit because as it turns out, in 2281, the Brotherhood of Steel's war with the Outcast Rebels is still apparently a major issue, even 4 years after Fo3.

"However, news of the civil war between the Brotherhood of Steel and Outcasts has reached other Brotherhood chapters, such as the Mojave Chapter"

I don't necessarily think 18 is important. Seeing as this is the fallout world and not our own but I do believe he would have to be around that age(16 and up) for him to be able to command. Unless he had zealot followers. You do have very interesting points though. Like I said before however, from past experience you can't trust developers to have smart stories. Or characters with real world logic, like if this then this. I see Beth more as just trying to throw winks in for the hardcoe fans. Was all that cannon? I would imagine Beth would atleast follow cannon

http://www.charts.noaa.gov/OnLineViewer/13270.shtml.

Note an area labeled Anchorage for Explosives (Area 5 on the map) ....

also

https://en.wikipedia.org/wiki/Boston_Navy_Yardand The Naval annex, given that both were still operational post 1950 its possible that it was in continued operation untill 2077 in this timeline.

Just a reminder as to why China would drop a nuke into the harbor.(and why said harbor would be a radioactive mess long after the fact)

In fact. . .

Exactly how much time do you think is actually spent pre-war? I think it'd be cool to live a day or two not just wake up day of.

During Fallout 3, Maxson was already a Squire, which is actually above the rank of Initiate in the CWBoS (see http://fallout.wikia.com/wiki/Brotherhood_of_Steel_ranks). He would also appear to have had at least some field experience, even though he was only 10 years old, and claimed to have killed a super mutant and accidentally shot and injured Sarah Lyons in the process. Lyons herself was a Sentinel at the age of 26, and was in command of her own unit. Move forwards to 2285, and an 18 year old Maxson could well have achieved a fairly senior rank, if he subsequently proved himself worthy on the battlefield. Lyons would most likely have succeeded her father, who could have either died due to his age, or ended up being killed during some conflict or other. Note that both Sarah Lyons and Star Paladin Cross have already featured in Fallout Shelter, and so are almost guaranteed to show up at some point during Fallout 4.

In the https://www.youtube.com/watch?v=Sn0UuTSE5XM I referred to earlier, it is suggested that the airship we see in the footage could have been built from scrap obtained in The Pitt. Of huge importance here is the fact that this airship in question bears the Lyons insignia, and not that of the Midwest. This insignia can also be seen twice in the concept art as shown http://www.gamesas.com/topic/1524192-more-clues-in-the-concept-art, once on the BoS soldier in PA (who I believe is actually Maxson), and who is fighting alongside our protagonist and Preston Harvey, and once on the cloak pin of an individual who looks suspiciously like a slightly older version of Maxson and is wearing BoS robes.

And so the CWBoS could well have built the airship as a means of expanding territory, and also as a faster method of travel than simply walking everywhere. Note that veribirds would likely have a far shorter useful range than an airship. If 8 whole years have in fact passed since the events of FO3, then the conflict with the outcasts could well be a distant memory. Tying all of this together, we can very realistically assume that something very important happens either just before or during Fallout 4's main quest that causes Lyons BoS to travel up from either Pittsburgh or Washington. And I have a very strong feeling, based on dozens of direct and indirect hints in the footage, that this 'something' is the outbreak of a full-scale war in the Commonwealth.

EDIT: as for the East/West connection, I am simply suggesting that the devs would likely leave options open for future Fallout titles from Obsidian and BGS.

So does Amata, Butch, James, Tenpenny and Mister Burke. It means nothing.

It all depends upon when Fallout 4 happens, if it is 8-10 years then I expect Maxson to at least be a Knight (if not higher rank) since he is already a Squire in F3 and Sarah Lyons is apparently personally training him so he is obviously being groomed for high rank within the military arm of the CWBOS.....in effect the present military leader is training her eventual replacement.

Lyons' CWBOS symbol on the airship seems to suggest that the airship is CWBOS and it shouldn't be that much of a surprise that CWBOS have the capability since MWBOS built their airship using the knowledge of the West Coast BOS and CWBOS (if the good route in canon) are sitting pretty as the regional power in DC, with lots of captured tech and the probable support of the local population allowing them to support and recruit greater numbers. Building an airship with the already establish BOS knowledge of how to build airships, shouldn't be beyond their tech level.

Why they are in Boston my be as simple as what is in Boston, the Institute with all that lovely pre war and new post war tech, that level of tech is going to draw the eye of any BOS faction worth the name....especially if that tech is under threat from an outside force.

I just wanted to point out that is not a fact. I am assuming you got that quote from one of the wiki sites. The source of that information would be Veronica, and in her description of a Brotherhood Chapter that had a "civil war" she doesn't specify what that chapter is. It is an assumpion on the part of people that it could be a reference to Lyon's Group and the Outcasts, but it could just as easily be a reference to the MWBoS chapter that broke off years earlier, or an entirely different chapter in the west.

So, Outcasts and Lyon's group may not be fighting and just continued on their separate ways. Regardless, it is not a fact they are fighting, and like many other things on wiki sites, they are not fact, but speculation.

Other than that, I agree that turning 18 doesn't signify anything in the BoS. Rank is gained by deeds, service, not by age or name. It makes more sense to me that Maxson, if he was 18, would be a Knight, and not even close to being a Paladin, and most definitely not leading missions, which would be reserved for seasoned veterans, who would be Paladins.

This is exactly my point. His rank would be determined by his deeds.

The whole idea behind my theory is not just that Maxson would have reached advlthood, but also that he would have eight years of military experience behind him by this time. And as Helljumper stated above, he was being personally trained by a Sentinel, and so he obviously showed signs of enormous potential. He may even turn out to be something of a prodigy when it comes to combat prowess and decision making, and so his rapid development into a leadership position would make perfect sense. This would explain him not only being given his own airship, but possibly even commanding an entire unit as Lyons had done during Fallout 3.

EDIT: remember also that during FO3 our protagonist, in spite of their achievements by the end of the main quest, was only 19 years old and fresh out of the vault.

Well, can't compare the super hero LW to a game NPC. Mainly because we don't know what the canon LW was like. Could have totally svcked at combat and mostly used their wits. Despite everything the LW did, the BoS also didn't put them in charge and make them Head Paladin.

I also highly doubt he has 8 years of military experience. It isn't like he gonna start going out into the field at 11 years old. MAYBE they would allow him to go out at 16, more than likely he would just be starting his military operations at the age of 18. The Wasteland is still a dangerous place, and they are not going to risk sending a 12 year old out into the field. Hell, he couldn't even fit in PA.

So, MAYBE 1 or 2 years experience. The vast majority in BoS don't become Paladins until they are about 30 years old.

Maybe the MWBoS and CWBoS have formed an alliance? They both seem to be somewhat more "progressive" than the traditional BoS.

There are many examples throughout history that show the exception rather than the rule in a situation such as this. King Tut, for example, became Pharaoh at 9 years old, and was only actually 18 when he died. And Joan of Arc led the entire French army to victory at the age of 19.

And so it is still possible for Maxson to be in a position of leadership within the CWBoS by the time he is 18 years old.

Put the pipe down, I'm close to having a stroke reading all of this.

Well, my hope is that both are in the game or at least lore on both in the game, and I do hope the game is set a few years after 3.

It usually isn't wise to base a theory on exceptions rather than rules. Sure, it a game so they can have these whimsical rare occurrences, but that isn't necessarily good writing and often times is just eyebrow raising. So, imo, it would be stupid to have super hero Arthur Maxson, the boy King who at 18 is Paladin and leading armies. That, imo, would be dumb as hell.

It doesn't matter to me if he is in the game, and I do hope it is years later(and both MW and CW BoS are in game) and not 2277, but if they make him boy king leading armies.......uggggggg.

We cannot really compare today to the fallout world for what age Maxson would have to be to command an expedition to Boston, he appeared to be getting military experience when he was only 10 years old and has apparently grown up his entire life being trained and groomed for military command, combine this with power his family name has within the BOS and it would be surprising if he wasn't an experienced soldier and leader (if he is 18-20 years old).

I'd expect once he was old enough to operate Power Armour he was probably in the field getting hands on experience......that is a question, is there a height requirement for Power Armour?

My point is that Maxson isn't from a normal culture, he would have spent his entire life under military training and discipline and was likely in the field getting hands on experience at what today would seem a young age. So I could see him leading his first independent command, probably with a older experience second in command to guide him.

Also senior Knights seem to be ones usually in command, I think CWBOS tended to mass all their Paladins into Lyons' Pride to provide them with an elite force who's reliability wasn't in question after the Outcasts rebelled....they are in effect a palace guard/royal bodyguard to Lyons and his daughter.

I guess it all comes down to that '200 years' tweet which suggests that Fallout 4 happens around the same year as Fallout 3 and the interview answer saying that Fallout 4 happens most after Fallout 3.

New Vegas is of course set in 2281, so is Fallout 4 the first Fallout game to be set before a previous game?

That same symbol is used by the Mid-western brotherhood.

http://fallout.wikia.com/wiki/Brotherhood_of_Steel_(Midwest)
http://fallout.wikia.com/wiki/Brotherhood_of_Steel_(Capital_Wasteland)

The gears are in the same exact position.

The insignia from the Midwest, as per your link, is actually inversed (blue cogs, white background) compared to Capital Wasteland (white cogs, red background). The insignia on the airship is therefore still consistent with CWBoS, as the cogs are a lighter color than the background metal of the airship.

Note that the insignias as referenced in the https://www.youtube.com/watch?v=Sn0UuTSE5XM are actually the ones shown shown http://fallout.gamepedia.com/Eastern_Brotherhood and http://fallout.gamepedia.com/Lyons%27_Brotherhood_of_Steel.

I would say that the consistant use of T-45d and it's upgraded T-60 variant are probably greater factors pointing to it being the Lyon's BoS. If you actually require evidence that is rather than it just being obvious which I think it is.

True http://fallout.gamepedia.com/Eastern_Brotherhood but the MidWestern Brotherhood also have the original BOS symbol layout, tactics is kind of confusing in that they have it appearing both ways, sometimes in the same picture. There are also several 'offical' versions of the MIdwesternBOS symbol.....most however have a blue symbol.

Lyons' BOS's official symbol is correct for the airship and is white the usual colour for the Lyons' BOS's symbol.

The BOS members now have the same symbol on their armour http://i.imgur.com/ST7umnC.png, instead of the original layout found in Fallout 3, it is however like Fallout 3 white like all the other examples of Lyons' BOS symbol.

Personally I'm a fan of the Midwestern BOS and i'd love them to be in Fallout 4, I'm still hopeful of a possible appearance as the opponents of Lyons' BOS, fighting over the Institute's tech.