Elves generally live 3 to 4 hundred years, but 500 is not out of the question for ones that take very good care of them selves. think of it like every 50 years for a human is 20 for a mer, it just so happens that the live styles of the Dunmer and Bosmer allows them a shorter life in most cases, as Altmer often enjoy the highest quality of life, without heavy red meat (as well as other people) diet of the Bosmer, and the extremely salty (salt rice, kwama eggs, and scrib jerky) diet of the Dunmer, Wizards like the Telvanni have a number of ways of extending their lives, though the most known method appears to be the draining of youth also practiced by the Mabrigash as seen in the legion questline in morrowind. For Altmer it is probably more living life in a slower stride as Pynaster prescribed.