In order to purchase a fully automatic weapon in the US, it must have been manufactured and NFA registered prior to the passage of the Firearm Owners Protection Act of 1986. Any fully automatic weapons manufactured after that date may only be transported to you if you are an FFL dealer with the appropriate Special Occupational Tax stamp, and a law enforcement letterhead authorising the transfer to you.
However, most "automatic" handguns are actually semi-automatic, not fully automatic. Those are legal, and in the US, regulated as ordinary firearms.
Yes.
You will have to specify if you are talking about single shot, revolver or semi-automatic and for what purpose.
Colt.
In the US, you must be 18 to buy a rifle or shotgun from a dealer, 21 to buy a handgun.
In the US, to buy from a dealer, Federal law requires you must be 18 to buy a long gun (rifle or shotgun) and 21 to buy a handgun. In some states, you may buy a handgun at 18 from a private seller, but not a dealer.
Yes, it is a semi-automatic.
Unless you tell us what type of handgun, the question can't be answered. Single Shot? Revovler? Semi-automatic? Black powder? Center fire? Rim Fire?
100 or so
Impossible to answer. There is no registration of gun owners in the US, so no records for the information you ask for. Best estimate is several million.
It is a type of pistol that was created by John Browning in 1911. The standard US Army 45 caliber automatic pistol was a Model 1911.
50-250
No, it is not legal to buy a handgun at the age of 18. The minimum age to purchase a handgun in the United States is 21.