Yeah, because no one would ever enter a false birth date.
Also, there is some advantage to the Teen Forum being seen by non-teens. Troubling posts can be spotted (someone being abused or suffering from an eating disorder or whatever). Also, many times, things are posted there, but are later moved to an open forum after someone notes that the person's post would get more responses if it weren't in the Teen Forum. As for why VB
"needs" the forum, of course it's not an essential item (none of the forums are, really). However, it's a nice place for teens to chat with others their own age. Might wanna knock that chip off your shoulder, dude.
Others have already mentioned the "new to vegetarianism" forum being for the almost veg*ns. Michael has the forum description reading "New and potential vegetarians can ask questions here." I don't think people are jumping all over potential vegheads there, but "potential" is a key word, I think. We've had several people lately whose attitude has been "I'm eating chicken, and I don't plan to go veg, but I'm doing something for the environment. I know this is VeggieBoards, but it's my right to be here, so up yours." *Those* folks have other websites that they can visit aside from Veggie