I believe that 21 is a terrible age for the introduction to Arms. That however is Texas law for purchase of a handgun. I am not sure exactly how strictly that is enforced though. I don't remember a time when I didn't have guns around. Even at school, we had shotguns and rifles and yes- the occasional pistol for target shooting after school (in our cars). I don't think anybody would have cared about the rifles or shotguns, but the pistols would have gotten us in a lot of trouble (this was pre-Columbine). Still- they'd have only called our parents who would have said- yeah- they're going to the range after school. Then they'd have to come pick up the guns. Nobody would have gone to jail.
I reflect back on how awkward it was to return from the first Persian Gulf War only 20 years old and having to have my mom (who flew out to NC for my return) to buy my beer for me. I believe if you're old enough to handle howitzers, high explosives, and yes- machine guns as a daily part of your life, then you are old enough to handle them at home. When somebody does something stupid, you punish the stupid-doer, not the whole society.
That's another thread. Back on topic, I have never felt too restricted by the Texas laws, but then, I am white. I sat in a gunsmith shop and heard with my own ears that it was OK for me to carry because the unspoken rule is: "If you're white and polite, it's alright." That is a quote. Perhaps our laws are very restrictive and selectively enforced which is the essence of all gun control laws.