I do not know where the OP lives. That being said.....
By federal regulation/laws, you must be 21 to purchase a handgun or ammunition made predominately for a handgun from an FFL holder. You can build an AR 9mm rifle, in most states as far as I know, and be legal. But you can not purchase ammo yourself from an FFL.
In Texas, it is perfectly legal for an 18 year old to own, be in possession of or buy a handgun from an INDIVIDUAL, but not an FFL holder. You can even carry it in your vehicle if done according to other state laws concerning carry of firearms.
Good advice,,,check your state's Penal Code, Government code and family code. That is where most firearm laws are in Texas anyway. Then check with a criminal lawyer. They will tell you what the applicable laws are as well as what they can defend you against.
The laws vary greatly from state to state.
And never, ever under any circumstances post publically anything that might even suggest you even might do something that even might be taken as ILLEGAL in any state.
Bad JUJU.
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