In GameFAQs, the minimum age limit is 14. (correct me if I'm wrong)
Just checked, it's 13 at GameFAQs too.
Putting an increased age limit on things isn't going to help a lot at all, actually. I've seen some children that are wise, smart, and/or mature, and I've seen immature, stupid, and foolish adults. It'll help a little, but in the long run, stupid people are just going to keep coming in. And besides, children can lie about their age rather easily so it kind of nulls the whole thing.
A test given to a registering member while they are registering could work, to see if they know the rules and how to act well enough. This has its problems, though, like people just looking up the answers or cheating.
And putting a rule requiring good spelling and grammar might also work, too, although I could see some things wrong with this too.
And most members are rather...meh at first, they get better as time progresses and as they integrate themselves into the community. And the further they go in, the more they learn about the community itself, what to do, and what not to do.
/logic and reasoning