I am also curious about this.
I will be 21 December 8th. PA law says to purchase from an FFL one must be 21 (handguns). to own a handgun in Pa is 18. This means that if my father bought me a gun and gave it to me, that would be swell. well, parents divorced, so that's not happening.
I have two firearms on hold (an AR15.com member who does FFL and NFA stuff much cheaper than store ffls nearby). I am waiting until I am 21 to pick up the guns (Kel-Tec p32 and Walther p22). Now I guess in my situation, I am purchasing from an FFL, so I have to wait, but if I was buying from another ar15.commer, or another person, I believe there is no law restricting person to person sale in PA/on the books... =)
www.packing.org has good info on pistol ownership laws... =) check out your state and read the quoted state laws part(s)
Ben