Is that why you need your parent's signature to enlist if you are under 18?
It is relegated to sexual consent. No troop suffers double jeopardy if his sexual partner is 14 or above. If the sexual contact is made on a US there can be no charges filed at all. In other words, although a civilian court may find him guilty of a statutory rape charge the military, thus the USA, does not recognize that charge and the troop can continue his career unabated upon return to service. The military will not press any charges against him. In many other cases the troop has to deal with a civilian court and then again deal with courts of military justice. It's called double jeopardy.