Elven races are capable of living centuries without the use of any magic I believe. I understand what your saying, about transferring your character from Oblivion to Skyrim. I don't like the idea of it however. Your Altmer could very well be alive, but someone's Imperial would have died from old age two centuries back. It wouldn't work for gameplay reasons.
Actually, as mentioned above, the Champion of Cyrodill, Ascended to become the new god of madness, the new Sheogorath, possibly gaining Deadraship and very likely gaining immortality. This would make it so that a) race shouldn't matter, he/she should still be alive but B) the ascension to Godship would make them literally unable to step foot on Tamerial and thus stuck in the Shivering Isles.
Maybe he was in prison for literally 200 years and all his skills went down. He'd suddenly get out and realize he's got no land-legs! Or something. Like maybe you can't practice your magic in prison or something. And he forgot to lift weights.
Wouldn't that mean they would start with literally capped thief skills tho... also there is that whole getting svck in the Shivering Isles bit as the new Sheogorath since the old Sheogorath reverted to being Juggalag(sp)