I'm 30 years old. I still get carded but people shouldn't flatter themselves when they do. It's more of a CYA thing than someone thinking you look like you're 21 or under.
I'm 22 now. Already wasted 8 years of my life posting stupid shit on the internet.
I've been on various messageboards now since I was 12. At first you think "wow that sucks" but then I realize that I wasn't going to do anything productive with that time anyway.
Honestly when I was a teenager, I assumed I'd get the fuck off the internet when I went to college. When I was in college, I assume I'd get off when I got a salaried job. Now I just figure that I will always hang around some type of forum so fuck it, who cares.