In your games, how relevant is PC age?
Is it just color, so you have a handle on how the PC looks and his or her background or experience?
Is it game-mechanically enforced, like in games like 1st-3rd edition GURPS, AD&D, Wizardry, or Traveller?
Is it something you totally ignore as irrelevant to play?
Is aging something that gets inflicted on PCs as an attack, a consequence of decisions to travel long distances, or otherwise modified in play?
I'm curious. My DF game doesn't pay any attention to it (people write it down, I look, the PCs die in a few short years anyway). It doesn't get inflicted on anyone or affect anyone in a negative way. I've had it matter before (mostly with players running too-young PCs who got treated as inferior to adults). I have a cool adventure that depends heavily on temporary aging (well, temporary if you win). But generally, it's not a big deal.
How about in your games?