Anyone under 21 shouldn't have a gun. End of story.
This is a little off topic, but after that elementary shooting, i think it's kinda ridiculous how parents blame video games for the violent acts that occur. First of all, kids shouldn't very well be playing rated M games. The only reason video games would have an effect on a kid would be because the parents were too stupid and bought their 5 year old a rated M game.
In my personal opinion, kids learn from watching their parents. Parents need to grow a pair and admit that it isn't videogames teaching their kids violence, it's usually themselves.
Enough of my rant. On topic, anyone under 21 shouldn't have a gun. They can't use someone else's gun unless they've had permission, and if there are guns in the house, they should be in a safe where only the owners of the guns know the combination. In addition, they should need some sort of permit. Besides the obvious concealed weapon's permit.
But then again, if someone is mentally ill, and dead set on killing people, they'll find one way or another no matter how strict the law is.
Avy & Sig credits go to Hurricane0