It's a bad idea to raise the minimum age for buying long guns. It's an even worse idea to arm teachers
It’s not as screwy as arming teachers, but increasing the legal age for buying a rifle or shotgun from 18 to 21 is also off target.
If the aim merely is to prevent anyone under 21 from possessing a military-style assault weapon, it won’t work and doesn’t make sense. There are millions of such firearms...