In the UK you must be a member of a registered gun club before you can even apply for a licence to hold a gun. In the USA anyone can buy a gun,you do not need to be a member of a gun club to own one, it is the opposite of the UK.
However as I just said, Gun club members are going to have had some training in safe use of guns so they are actually better than the ordinary person who just wants to have a gun.
Anyone over 16 or 18 can buy as many guns as they want in the USA, as long as they have not got a criminal record , that is why the shop is suppose to check your ID. Private sellers of guns are supposed to check buyers ID but few bother.