Gonna have to agree with Tekla, you can ask for more independence, but if they don't want to give it to you, that's their call if they're feeding you, providing you with a place to sleep, buying your clothes...etc...
My only exception to this is if you're a student and have a part time job and do your part to pay your way through school. If you're living at home to cut expenses there, you're parents should cut you some slack because you're attempting to make something of yourself...this is the current arrangement I have. I work, drive myself to school and work, pay for gas, pay for a decent amount of food, all my clothing and put money in an account for my education that if I were to ever stop going would just go to my parents as rent. And obviously if you are living there and paying rent, you're essentially paying for more freedom. But if you're not contributing to expenses, you have to work with them and try to get them on board with you rather than just throwing the "I'm 18 I can do whatever the heck I want"
However, that's not to say that they are obligated to cut you some slack.