whether or not the OP is on the level, some states may lay out how lawful transport may be arranged. in my state, an 18 yr old can go shooting at the range. what they can't do is stash their handgun in the glove box, or console, or under their seat. it needs to be transported in a 'case designed to transport a firearm', and be unloaded.
had a 19 yr old at the range one day who asked this very question. he had two or three handguns he'd inherited and thought he couldnt shoot them until he was 21. an officer from the Anchorage Police Department was on the range, and he confirmed the possession of a handgun by someone 18 or older to be lawful.
whattsamatter WA? aintcha never heard of a beretta storm? that a carbine rifle. also chambered in .40s&w and .45acp. and the marlin lever guns, they can be in .357 mag, .44mag, right?
which is why the fine people working checkout registers for walmart ask the question 'is this ammo to be for a handgun or rifle?' when the purchaser appears to be under 21. otherwise, they'd just say 'nope, you cant have any ammo that MIGHT be used in a handgun.'
