Just like anywhere else, 18 for a Title 1 long gun, 21 for a handgun and NFA restricted items, clean criminal record - no felony convictions, no convictions for domestic violence (misdemeanor or felony), no record of having been adjudicated mentally defective, no dishonorable discharges from the military.
At a minium, 21 for a hand gun and 18 for a long gun.
18 or 21 depending on if you are buying long gun or hand gun ammunition
Hand gun - 21; long gun - 18
As long as you meet the legal restrictions on gun ownership, if you purchase a gun you can pay for it with any method of payment.
21
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.
It depends on your meaning of "have". To purchase a paintball gun the legal age is 17. Though if you have an adult present, you may purchase one at any age. So in theory, a 2 year old could have a gun.
Yes you can. ORS 266.170 In Oregon an expungement in relief from prohibiton of gun rights.
18 for long gun, 21 for hand gun
Since you posted the question on the internet, do an internet search on Maryland gun laws.
Federal law mandates that you be at least 18 to purchase a long gun.
It's legal to purchase a gun out of state, but the gun is supposed to be shipped to a dealer in your state, and you have to go to THAT dealer to pick it up.