It depends on what you mean by license, and where you are located. If you mean a permit to carry a gun, in most U.S. states, the minimum age is 21.
that depends on what state you live in for instance in Massachusetts you need to be at least 18 but in states like New Hampshire you need to be 14.
You will have to contact your local police. NY has a patchwork or laws.
18 but if you are under 18 but over 12 you can have a minor's license where you can't purchase a gun but you can use one and buy ammunition.
Contact your local police for current information.
As far as I know you have to be at least 18 to buy a gun. That's what it was several years ago anyway, don't know if it has changed now.