I realized I was old when I went to an Applebee's a few years ago and Rancid was playing on the Muzak station. I immediately ran to the bathroom and found a couple of gray hairs, then a part of me died.
It's not easy realizing that you're old and irrelevant to popular culture. But with the way that popular culture is getting now compared to how it was when we were kids, I think that might be for the best.
For instance: Today I was watching a long collection of Beavis & Butt-head music videos and remembering when they were the "worst thing on TV", pastors were complaining about them; and a clip came up where they started making fun of a Marilyn Manson video and I immediately in my mind shot back to the eight grade when I was put in In School Suspension for reading the Marilyn Manson autobiography during silent reading time: He was every parent's nightmare because of the album "Antichrist Superstar" and now he just seems so tame and even kind of satirical when you go back and watch some of his videos. It makes me remember how my parents used to say when I would listen to him "Oh he's just doing the Alice Cooper gimmick!" and then they ended up exposing me to the "shock rockers" of their age, like Twisted Sister, Alice Cooper, and David Bowie.