Eugene Volokh asks and interesting question about how hard it would be for 18-20 year olds to get a handgun. Federal law prevents anyone under the age of 21 from buying a handgun from a federally licensed dealer, but in most states 18-20 years olds are permitted to purchase and possess firearms under state law.
It would indeed be a straw purchase for someone to purchase a gun from a federally license firearms dealer on behalf of someone 18-20 years old, because you are not the actual buyer. It would, however, be legal for a parent to buy one for their 18-20 year old as a gift, I believe. In a gift situation, you are the actual buyer, even if you’re not the person to possess it in the end. In Pennsylvania, private transactions of handguns are unlawful, but the County Sheriff is one of the authorities that can process a transaction. Since he is not a federally licensed dealer, and PA law allows for possession of a handgun by someone 18 years or older, I would presume a Pennsylvania Sheriff would be able to process this transaction. It would still, presumably, require a PICS check, but since the transaction is not federally regulated, no 4473 should be required. So I believe an 18-20 year old could still get a handgun in a private transfer, even under Pennsylvania restrictive transfer regime.