Womanhood, sex and relationships

Why are we told what we can and can not do with our bodies? I understand parents not wanting their teenagers having sex, but what ever happened to making our own choices? After all, it's your body, and in the end the person you will be causing most effect on is yourself.. I'm  not saying having sex is right at a young age, but having a right to what you do is. It's not something to be hated for and its something to be educated about, but all in all it is your right because it is your body. Say the circumstances were opposite.. What if your parents wanted you to have sex early and you didn't want to.. Think about it