Hehe, good one. I'll tell you when I first felt old.
I was playing basketball with some guys who were all around 21. I had told them I was 37 (this was 3 years ago). At the end of the 3vs3, the yougest healthiest guy challenged me to a 1 one 1. When the game was nearing the end, and I was kicking his ass, his freinds yell out to him, "Hey, are you going to let that guy beat you, he's almost 40!!"
My head swung around a few times, as if I was looking for someone else who could be "almost 40" then the sad realization hit me hard, I'm almost 40, crap. At least I won the game.
The other times I feel old, is like when you bring up old TV shows. I got a kid now who is 22 working for me, and I started to do the sound effect from the bionic man, as we were lifting something very heavy, and he just didn't get it. When I started to explain it to him, I realized he probably wasn't even born yet when that was out.