There are legal loopholes you can exploit to get yourself a lower.. There are legal ways to acquire a lower.

The first and most legally sound option( as far as I can tell IANAL) ~~is to make a 80% lower. While you cannot buy, a pistol until you are 21from an ffl under federal law, ~~wether you can possess one is a bit of a gray area under federal law, but if you build your 80% lower into a rifle you are compliant with the law. The only caveats to this is that you have to use your own tools, you have to do all the work on the lower yourself, and it’s probably illegal in some states(I’m looking at you California, and New York ) Another upside is that there a lot less of a paper trail, and it would be much harder to prove you owned a firearm. *irrelevant as it is perfectly legal Method two is a bit more dubiously legal depending on how you do it is perfectly legal. In most states a family member can gift you firearms without it being a straw purchase as long as you don’t ask them to buy it for you. But you can run into issues with state laws. You also can do it wrong and it can become a straw purchase. As far as I can tell the way to do it would be to have a family member who is over 21 buy the rifle and assemble it(I think you could help but idk) and after it’s finished you take it to a FFL and buy it from them and have it transferred at an FFL From what I can tell if you transfer it from one family to another, through an FFL and do background checks and the whole 9yards you can get away with what is basically a straw purchase, but it’s not because the AR is a rifle when it’s transferred and not a stripped lower They can just give you your lower as a present. Anyway those are the methods I have come up with do build on legally as far as I can tell BUT I AM NOT A LAWYER

I am a lawyer, but not your attorney. This advice doesn’t constitute a legal relashionship