I'm not going to argue on that one. If anyone can't get on board with raising the age limit to buy a gun, any (real) gun, to 21, isn't coming to the table with honest intentions. Again, it's hard to get past the fact that we as a society have agreed that young people under 21 aren't responsible enough to buy alcohol, but they're somehow responsible enough to buy a firearm. That is an obvious contradiction that needs to be addressed.
Hell, after watching my 17 year old drive, I question whether or not they're responsible enough to drive a vehicle before 21.