Experience for advancing levels isn't really related to time at all. It is related to overcoming challenges. An 80 yo man can be first lever, as could a 700 yo elf.
Similarly, if I reach 20th level as a 19 yo kid, it will be pretty tough for me to advance, because things that can challenge me are very rare.
Basically the Pathfinder/D&D experience systems is focused on characters facing and overcoming a fateful set of challenges (what we call a campaign) and becoming legendary heroes from conquering these foes. It doesn't really have much to do with time spent studying and similar concepts.
If you're replying to me, I never mentioned gaining levels, but maintaining them. I mentioned at the start that the system doesn't have an accurate way to simulate "being rusty from lack of training" or "forgetting stuff you haven't used in a long time". So I proposed that typically, adventurers need to set some time to keep themselves in top shape, whether physically or mentally. An elf, no matter how long-lived, cannot maintain the required amount of training that justifies a full BAB, 9th level spells and all of the standard magus class features.
It would be a lie if I said I did not have elder Elven caster NPCs in my homebrew that ignored some class mechanics because their ages suggest they should.
EDIT: derned double negatives!