To purchace a long-gun (Rifle, Shotgun, ect.) you need to be at least 18 and not a Felon, you also need a valid ID, also some states and even cities may have restrictions on types of rifles you can buy so make sure to check your local laws. To purchase ammunition you need to be at least 16. I'm not sure for handguns, all I know is that you need to be at least 21 buy their are probably more requirements.