Before you can legally sell a privately owned firearm, you have to have legally purchased it in the first place. Gun shop owners must possess a Federal Firearms License in order to sell guns. The following are key factors regarding purchasing a gun in Ohio: You must be at least 21 years of age to legally purchase a handgun in this state. (This is important to remember if you are selling a gun to another person.) You may buy other types of firearms once you reach age 18. You cannot be under the influence of drugs or alcohol when purchasing a firearm at a gun store. You may buy a gun (if you meet all other criteria) from a federally licensed gun shop owner or a private seller. Depending on the situation, you may be required to undergo a background check before purchasing a firearm.