Winchester+ Filter
I started learning my magic long before eighteen. So, I can see how changing the age limit can be a good thing. Some of these kids should learn how to defend themselves. That being said, I'm sure there are some kids out there that aren't mature enough for it, so you might want a stipulation somewhere in there about if they decide to screw around.
And I'll agree with Chuck and the sixteen bit, younger than that dealing with weapons is kind of scary.