Assault rifles can be purchased in many states in the United States. They are illegal in a few states with special laws in some smaller jurisdictions.
Have never heard of an underwater assault rifle. In the US, you must be 18 to buy a rifle, and 21 to buy a fully automatic rifle.
You will need to define assault rifle, and where you live. A TRUE assault rifle is a machine gun, and transfers of them are tightly regulated by the Federal government. What most people CALL an assault rifle is nothing but a semi-automatic rifle, and in most of the US, does not require a license to possess.
18 to buy a rifle or shotgun, 21 to buy a handgun or assault rifle.
No.
You can buy a semi automatic Title I rifle at 18. To purchase a true, select fire (auto or burst) NFA tax stamped assault rifle, you must be 21.
A TRUE Assault Rifle is fully automatic. Federal law requires you be 21 to buy one of those in ANY state. However, what people may CALL an assault rifle (such as a semi-auto AK47) can be purchased at 18.
You can buy them in Canada and in countries in Europe which allow them, but they're currently unavailable in the US, due to 922r parts count laws.
Yes
You must be 18 to buy a rifle. The stock has nothing to do with it.
About $1,000 US. But you cannot buy it in the states as a law banning Chinese guns from importing into the U.S.
For a transferrable, select fire, NFA tax stamped rifle, 21. For a semi auto military styled rifle, 18. This law pertains to the US, and laws will vary in other countries.
Assault rifle.