You can't enter into a legal contract with a minor.
You can get married before 18, at least in Florida, with your parents consent. I used to have a young lady that worked for me. She was married at 15 and got a court order declaring her no longer a minor, so the labor laws applying to minors didn't apply to her (how many hours a day/week she could work, how late she could work on a "school" night, etc.).