I had a character who's backstory wasn't too far off from that. The career changes weren't entirely voluntary, though, and usually were because he had suddenly lost all his money and needed to go adventuring again to rebuild his wealth. By the time the campaign was set, he was close to a millennium old, borderline senile, and making some very outrageous claims about things he had supposedly done in the past, like getting into a bar fight with Selune during the Time of Troubles or having once dated Lolth.