That question is too vague. Most states are different and it also depends on what type of gun you want, ie. Shotgun, Pistol, High-Powered Rifle, etc.
In the US, 21 years old.
18 in the US.
Whether or not you can have a gun license at 20 years old depends on which US state you live in and the type of gun as the laws vary somewhat.
You must be 18 Years old to purchase one
You need to tell us more about the "gun license" and for what area. There are many different gun licenses.
You must be 18 Years old to purchase one
Gun shop, gun show, on line auctions
Depends on how the gun is carried, and what type of gun. You need to give us some information to get a meaningful answer. Every 18 yr old that goes deer hunting "carries" a gun in their vehicle.
Gun shop, gun show, on line gun forum, or post here giving us as much information on the gun as you can. Right now, we do not know if it is a rifle or pistol.
in the US, yes. You may make a gun for your own use. You must be old enough to possess a gun, and it must meet legal characteristics of a legal firearm.
Not in the US. You must be 21 to buy a submachinegun
Earlier gun than the Old West.