This thing was argued so many times a couple years ago.
I don't actually know what it says, but I thought it just meant that Badspot had to ask if the person is over the age of 13 or not? I didn't think it meant he had to turn away anyone under the age of 13.
Not sure though.
The act is to essentially prevent kids from being exposed to things they shouldn't be. Much like a rating for a game. Badspot so chose to just restrict the forums to anyone who was 12 or 13+. Though, I don't think it makes a difference what age you register as, because the terms of "COPPA" is that if it's a child under the age, then they just have to have parental supervision / parental consent to play.