What is the lifespan of a breton?

Untill he meets an atronach.

Damn reflect.

Longer than a man but shorter than an elf.

There's a passage that implies this in Brief History of the Empire:

When Cassynder assumed the throne upon the death of his mother, he was already middle-aged. Only half Elven, he aged like a Breton.

Which, I assume, means he didn't age at the same rate as his mother, being only half elven. So he aged like the next best race; a Breton.

I agree with Albides, although I would not place the aging square in the middle of the two racial averages. I believe that, although longer lived than a human, a Breton is closer to human aging than elven aging, mainly due to the Bretons being commonly seen as a predominently human race.

___TWM

I'd agree with that, but after Daggerfall, elves were given a more modest lifespan, anywhere from 120 to 200 years, excluding the use of magic.

How old is Barenziah? Isn't she several hundred years old? Although, she is royalty.
Overall, I'd agree that Breton's most likely live around 100 years.

Yes. She even met Tiber Septim. I can't remember who said it, but I've always like the explanation that elven lifespans are more "stretchable".

However, in Daggerfall, the Bretons are implied to age just as an other human would.

If we use Daggerfall as evidence, and at the very least we can say that Daggerfall is the undisputed source on Breton culture and politics (at the least) and these aspects of Daggerfall have remained unchanged after the numerous post-Daggerfall retconns, then we can assume that Bretons age in the same way the other human races do.

In regards to your quote Albidies, let us remember that Cassynder was half Breton and half Dunmer. Thus, the phrase "aged like a Breton" simply implied that he did not inherit his mother's long life and does not really imply that Bretons live longer then most men, but rather it actually implies they live the same span of time.

I'll concede that, but still think this may or may not apply after the PGE 1st Ed.