The whole 18/21 thing - - well - just like back in 1970 - old enough to fight, old enough to vote....old enough to die/kill for your country, you're old enough to buy and carry a handgun to protect your life.
(you should also be able to go into a bar & have a beer - but - that overstepping of federal authority is the topic of a whole 'nuther discussion)
(you should also be able to go into a bar & have a beer - but - that overstepping of federal authority is the topic of a whole 'nuther discussion)