Used to run a gun shop before the Army; any felony/prohibitive offense on your record will flag regardless of how old. We had dudes get denied and further hemmed up because of a DUI from the 90s they forgot about. Also when we would get a denial for someone, it didn't tell us why. Even if we called the PICS line (PA instant check system, supported by NICS) They wouldn't/couldn't tell us. Now also as an FFL we had a right and were encouraged to gauge the situation and make a call regardless of what the check says. If you didn't pass a vibe check we could just say your shit was denied, we weren't required to sell you a gun if we didn't want to. so that's probably what Fudd ass Leroy is on your shit about. Fudds love that excuse because they're afraid of anyone younger than themselves.
Above all else, fuck gun laws. Fuck 12. Buy a lower or off the shelf AR from a person to person sale and build a AR of your liking. Buy poly 80 glock lowers and build your own glock. Train with them and keep them a secret. There's always a way.