I often wonder what age is 'young' or 'old' for various races. Mannimarco is known to have lived for about 1000 years (ca.2E200-3E433) according to his Lore article on uesp, so clearly Altmer have a significant lifespan although perhaps 1000 is not typical (also, Mannimarco is defeated by the player, so it is possible his future lifespan may have been significant). Accordingly, my Altmer mage had the most youthful face possible but is still 87 for roleplaying purposes. I consider that 87 in Altmer years is probably equivalent to about 20 in human (ie Imperial, Breton, Nord, Redguard) years.
Dunmer and Bosmer I guess would have less significant lifespans but still greater than humans, as their archetypal lifestyles tend to be more active than sedentary (thieves/scouts/warriors as opposed to scholars or mages). Although, Barenziah lives for several hundred years if I recall. Khajiit I guess probably don't live all that long as in-game sources refer to 'litters' of Khajiit kittens, diminishing the benefits of parenting to them. Argonians, I would regard as similar to Khajiit. Orcs? Haven't a clue, but I never played Orcs, so

.
So, in my mind, lifespans are like this:
Altmer: ~ 500-800 years typical, potentially? perhaps 1200.
Dunmer/Bosmer: ~ 250-400 years typical, potential 600.
Imperials/Bretons/Redguards/Nords: standard human lifespans (50-80 years typical, potential 100 or so)
Khajiit/Argonians: 15-30 years, similar to real-life cats and lizards.
Orcs: ?
My own characters had the following ages:
Luther Martinus (Imperial Crusader): 35 - middle-aged appearance
Gwenyan (Altmer Healer): 87 - youthful appearance
Fenrir Darkblade (Dunmer Assassin): 45 - youthful appearence
Berrick (Redguard Mercenary): 21 - youthful appearence
Marie le Belle (Breton Rogue): 18 - youthful appearence
Eldod Ulthainn (Bosmer Archer/Scout): 52 - young middle-aged appearence
Aenur (Altmer Alchemist): 408 - late middle-aged appearence, but still with colour in his hair!
Kerr-Mitt (Argonian Scout): 8 - youthful appearence, whatever that means with Argonians!
Julia Martinus (Imperial Soldier): 38 - middle-aged appearence
PS. Acadian, I read and love Buffy's journal over at Chorrol.com, but one of the things that could be improved about it is to change her age to make it more consistent with relative Bosmer/human age. If I recall, one of the entries refers to Daenlin saying to Buffy that 'she doesn't need to rush through life like those round-ears'. Yet, at 18, she has already left home and is independent, and an accomplished adventurer, and is harbouring mature feelings for Savlian Matius. In my mind, an 18-year-old Bosmer would probably be barely out of nappies.