text: what are the laws for underage sex in mississippi, what age do you have to be when aren't a minor anymore?   the first part i not sure about. but in the us you have to be 18 years old before you are legally an adult. but somethings are still resisted till you are 21. like alcohol, some clubs, gambling (in some states) basically at 18 you can sign your 'own name' on documents, open accounts. you don't need your parents to sign your documents (contracts). unless it is a cosigning like a house or car, then you need an adult to sign with you. cosigning is when an adult says they are responsible for you paying. if you miss up it hurts their credit too