What is the average lifespan for all of the races? Including things like Falmer.

Humans - Talos lived to 102 or 106 or something. That's the oldest lived non-mage we know. Humans wizards can live for hundreds of years.
Dunmer and Bosmer - Commoners, about 250 years, nobles, about 300 - 400 years or longer. Mages can live to nearly a thousand years, if the mage is very good, they can basically live forever.
Altmer - Commoners(not really any commoners in Alinor, almost everyone there is a wizard of some variety.) 350 years, nobles, probably longer than 500 years, wizards, like Mannimarco, can live for thousands of years.

Altmer live longer than other elves because Phynaster(I hope I spelled that right from memory) taught them how to walk properly, like their ancestors, and thus won them what I'd speculate at a hundred or so extra years of life.

This

Also, Orcs have a short life expectancy at about 40-60 years.
Not sure about Khajiit and Argonians, but I do know that Khajiit kittens mature very fast so I assume they don't live as long as most races.

I forgot to mention.

Orcs live for very short times, around 20 - 40, I'd think, though I could be wrong. They might live to 50 or 60, someone will know better about this than me.
Khajit and Argonians probably live lifespans similiar to humans, Argonians maybe a little longer.

King Harald, the 13th King of the First Nordic Empire of Skyrim, and 13th in the line of Ysgramor, lived to be 108.

What about Bretons?

Bretons are humans, and fall under that category. They might live slightly longer with their elven blood, but I doubt it.

There was that one Nord (Not Heart-Fang who had the Ring of Hircine) you met in a sidequuest who was like 500 and wanted to find Sovengarde. Never did the quest, but what was the reason for his age?

Can't recall exactly where, but I believe I read that Breton's actually have a shorter lifespan because of their mix of elven and human blood.

Brief history of the Empire mentions that one of Katariah's sons aged "like a Breton" and was of poor health. When he came to power after 40 years of his mother's reign, he didn't even last half a decade.
I'm not aware of anything else, and this seems more circumstancial than anything.

Well my Bretons are powerful mages so who knows

It is also worth noting that while dunmer, altmer and bosmer all live longer than humans, it doesn't take longer for them to reach maturity. Barenziah became pregnant at 16 I think (although it was considered unusual) and the dunmer in "Interview with a Dunmer" mentions that he has served several decades in the Legion despite only being 50.