If you play a human and you RP the aging proccess then you will age out in a couple of years. But as was said above many players dont RP that they have aged. So we have human PCs that should be in their 80's still running about LOL.
For clarification, a character who should be in their mid-80s should not RPed as being in their 50s, number-wise... they are still in their 80s, you can't fudge that. There are just multiple reasons we can use for excuses to not retire them so soon - no one wants to make anyone quit their characters.