I use age restrictions on every server I run because I really don't want to be there the first time some kid figures out he can get a rise out of others by posting dumb crap.
Like racial epithets. Homosexual slurs. Misogyny. WWII-era anti-semitic holocaust jokes. Teenage edgy bullshit designed to get a rise out of anyone within earshot - because you know they won't like it, like empathy's goatseed evil twin brother. That shit wasn't really funny the first time I heard it (or said it), and I usually regret the times I played a part.
To everyone saying "OMG BUT I R DIFFERNT!!!!!"
Congrats, you might very well be a 1%'er thats totally different.
Do I want to take that chance?
Do I want to risk you getting a hardon for talking trash one day out of the blue and alienating a portion of my server?
Have I seen "Mature" kids lose their cool one day and snap off?
Just because your parents buy you Rated M games doesn't mean you are mature.
And honestly, the "Real" mature ones are typically smart enough to sort out how to get passed an Age Restriction.
Hell, one of my best players is a 15 year old from Ireland that even allowed to mod on the server because he was a better, more mature player than the 20 year olds.
He lied to me to get on the server though, and managed to play with me for about a year before I sorted it out. When I found out though, I banned him, and then held a poll on our forums describing the situation and all the members voted on it.
Pro-Tip: He didn't whine or cry about age restrictions. He went above and beyond to handle himself like an adult at all times.
He was a 1%'er