The life spans vary between races and between games. In Morrowind it was stated many times that the Telvanni wizards are hundreds years old and Dyvaith Fyr is about 4000 years old and in good shape, on the other hand, the Orcs and I think Nors have somewhat low lifespan due to some curse or some such. If magic plays any role, then the Altmers will sure have much longer life span. The question stands about the Breons since they are descendants of the Altmer and Nords.
that is correct, it depends a lot on race. One of the problems trying to draw comparisons to the Middle-Ages in this area encounters is that the Middle Ages didn't have elves, or magic, for that matter. Access to restoration magic, I'd expect, can do a lot to increase one's chances of living to an old age, if nothing else, it can be used to cure diseases and poisoning and heal wounds, thus reducing your chance of dying of such things, and though this could just be due to Bethesda not wanting to make the games too dark and gritty, one does get the impression that the general condition of living for most citizens of Tamriel is better than it would have been for the common peasantry in the Middle Ages.
Lifestyle must also be taken into account, of course, I'd expect the Ashlanders, for example, to have a lower average lifespan than settled Dunmer living a middle-class lifestyle, due to more exposure to the elements and such, as well as greater danger of being killed by causes other than old age. Whereas in Cyrodiil, the people of the Imperial City probably have a higher life expectancy than those living in Bravil, except maybe the Waterfront. But of course, the effects that different living conditions and life styles could have on the average life expectancy of people would also play a part in the real world.