No. You can't buy one, either by the true definition or by the BATFE definition. Connecticut is one of the states which wrote the Clinton ban into state legislature when it went into sunset in 2004.
No. Minnesota requires a transfer permit for handguns.
No
Yes
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.
In MOST of the US, a permit is NOT required to purchase a .22 rifle. IF one is required in your area, it is because elected politicians passed a law that says you need a permit. You would need to ask them why they did 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.
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 only need a license if you wish to wear a handgun openly or concealed (it is illegal to do either without a permit). But no permit is needed to buy or own any otherwise-legal gun (rifle, shotgun, pistol) or to carry a rifle or shotgun.
You must be 18 to buy a rifle. The stock has nothing to do with it.