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.
21 or older.
21
Yes. Virginia law does not prohibit a person at least 18 years of age from POSSESSING a handgun. However, FEDERAL law will not permit you to PURCHASE a handgun OR handgun ammunition until you are 21. Virginia law does permit certain person UNDER 18 to possess a handgun in limited circumstances (permission of parents, instructional class, etc)
In the United States, you can legally purchase a handgun at the age of 18 from a licensed firearms dealer.
To purchase a handgun from a licensed dealer, or from a venue at which 25 or more guns are available for sale, you must be 21+ To purchase handgun ammunition, you must be 21+ To get a CHL in Oregon, you must be 21+ To own a handgun in Oregon, you must be 18+ Private party sales are legal in Oregon, provided that both parties are legally able to purchase / possess the firearms in question (not a felon, above the legal age, etc.). In theory, then, a person above the age of 18 could legally purchase a handgun as part of a private party sale. They just cannot carry it, or transport it loaded.
18
Technically you can OWN one at any age. My father gave me my first .38 when I was 13. However to purchase a handgun from a licensed dealer or to get your concealed weapons permit you have to be 21. You can purchase long guns (any gun with a barrel length of at least 18") and ammunition when you are 18.
In most U.S. states, there is no specific minimum age to use a gun for legal purposes, but a person does have to be 21 to legally own or purchase a handgun.
Generally it is 21.
21
Virginia does not require registration, so the answer the question, assuming you are of legal age to own the gun and the gun isn't stolen, is no, you do not have to register it, because in Virginia, registration doesn't exist.