There's the other side of the coin as well. You hear a young kid talk and invariable some douchebag will say something like "Never use your mic again" or "Wait 'til your balls drop before you talk." I can't stand that.
I don't mind a kid talking on a mic so long as what he has to say is either useful, interesting, or genuinely funny. I've played with plenty of "mature" gamers who drone on incessantly about things nobody cares about, or just use their internet anonymity as a license to be the worst human being possible.