The "under 21 with a hunting license can get a longgun thing" is more accurately the "...can get a firearm that is not a handgun or a semiautomatic centerfire rifle" thing.
(a) A person licensed under Sections 26700 to 26915 [dealer], inclusive, shall not sell, supply, deliver, or give possession or control of a firearm to any person who is under 21 years of age.
(b) (1) Subdivision (a) does not apply to or affect the sale, supplying, delivery, or giving possession or control of a firearm that is not a handgun or a semiautomatic centerfire rifle to a person 18 years of age or older who possesses a valid, unexpired hunting license issued by the Department of Fish and Wildlife.