United States Federal Law 18 U.S.C. 922(x) Places The Legal Age to POSSESS a Handgun at 18 Years Old.
HOWEVER, United States Federal Law 18 U.S.C. 922(b)(1) Places The Age where a Federal Firearms Licensee may SELL a Handgun to a Person at 21 Years of Age.
BUT..., You MAY Buy a Handgun from a Private Person OR a Gun Show at only 18 Years of Age under Pennsylvania Law 18 Pa.C.S. 6110.1(a), as This Code Section Provides that it is ONLY Unlawful for a Person to Possess a Firearm if that Person is under 18 Years Old.
Pennsylvania is an Open Carry State by Default, which means that it is LAWFUL to Openly Carry a Handgun on Your Hip at 18 Years Old.