You have told us your age.
You are a minor.
It is against the law.
No means NO.
- A full explanation
In the United States, a 20 year old person is an adult. It is illegal for an adult to engage in sexual activities with a minor. Do your parents approve of it? It is also illegal for parents to encourage a minor daughter to have sex with an adult.
In short, you want to have sex with this person who is an adult and you are a minor. If your parents disagree they can press charges and issue a warrant to detain this person. In the other hand, if your parents want you to perform sex with an adult, you can report them to the authorities and they will be arrested.
No matter how you look at it, it is illegal either way. If you are a minor you can get a LOT of people in trouble with your promiscuity; your parents can be charged if you're found in a hotel with your boyfriend having sex. Either way you put it, lots of people want to save themselves from the responsibility; so all in all, the responsibility falls on ALL the adults who are involved with the minor.