The legal age to buy a gun depends on the type of gun it is. For an example, to buy a rifle or shotgun(excluding assault rifles) you must be 18 years of age. To buy a handgun you must be 21.
No, it is not legal to purchase gun magazines without a license in California.
No, it is not legal for a tourist to purchase a gun in California. Only residents with a valid California ID and proof of residency can legally buy a firearm in the state.
Hand gun - 21; long gun - 18
21
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.
18 for long gun, 21 for hand gun
Since you posted the question on the internet, do an internet search on Maryland gun laws.
18 or 21 depending on if you are buying long gun or hand gun ammunition
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.
18 for long guns 21 for hand guns.
Assuming you are of legal age to purchase, black powder or smokeless powder for reloading can be purchased from gun shops. Yes, proof of age is required.
Please specificy what you mean by "permission." If you are of legal age, you don't have to have anyone's permission.