I don't support an age limit. Maybe, like 16+ as a limit, but 30+ is too high. There's a forum I am on that is run almost equally by teens and adults and it runs great, with about 10,000 members and a great PG atmosphere. Age doesn't equal maturity.
I'd like a system like on Toontown, where if you know the person IRL or just outside the game, you could exchange a code and have non-restricted chat with that person. I don't know how that'd be implemented, but just an idea.