Federal law is 18
Legally, no. You must be 18 to purchase a rifle or shotgun, and 21 to purchase a handgun.
Yes the background check for guns is the same in every state
Yes.
Rifle or shotgun FROM A DEALER- yes. You may not purchase a handgun except in your state of residence, and any long gun purchased in another state must be from a licensed dealer (not a private person). The answer to this question has changed over the past several years, at one time you could not.
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.
Depends on Texas law.
Yes... I may be wrong about this, but I believe Delaware is one of the states where you must be a resident of that state to buy a firearm from there, although I could be wrong about that.
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.
In terms of a drivers licence or state issued identification card, yes. As for a licence to buy a rifle, no. You just need to show ID, fill out the Form 4473, and be able to pass the NICS criminal background check.
You must be 18 to buy a rifle. The stock has nothing to do with it.
18.
In the US, you must be 18 to buy a rifle or shotgun from a dealer, 21 to buy a handgun.