Just to have this said: Yeah, age restrictions are generalizing. Aye, you're right, theres sober, level-headed and calm youngsters aplenty. It's nowhere near fair being excluded just because one does not have a specific age, yet. But.
One thing that I did not read in this thread, that must be said is this: It's their server. Their money, their time, their tech.. their decision. They do not want players below a certain age and there is absolutely nothing one can do about it. Maybe they had problems with younger players in the past, maybe they don't like young people in general, maybe it's a severe youngphobia - whatever the case may be, in the end - they decide. A player has absolutely no RIGHT to demand to be granted access to a specific server, except it's one you payed hard cash for the membership (though who in their right mind would do THAT^^) and have bought said right.
Please note that I am aware that you, the TO, did not demand anything in this thread, even though the reason behind this topic is obvious. I just wanted to put that paragraph out there. And, age aside, 'People from teh Internet' often (not always) relay to some sort of "I feel I have the right to complain/demand/kick'n'scream, so there!" attitude. And that is, simply put, laughable at best.
Apart of that - wolfpax' statement has a whole lot of truth in it.