Every forum has age verification now, as I think there was a law passed about protecting children on the internet.
Sheesh, I was viewing internet pr0n by the time I was his age for sure. I turned out --mostly-- okay. I certainly wouldn't see any need to protect a kid from a paintball forum.
I mean, he could be looking up how to build a pipe bomb or a zipgun. And I DONT THINK a site that is sharing that kind of information has an age-check!
It's not about the content of the forum, but rather communicating with others(ie the potential for the child to give out their personal information) I think.