thoughts on authority.

I've been wrestling with a few ideas tonight and I'm still not sure where I stand. I'm going to try to explain this with as few details as possible, so hopefully it will still make sense. I have been faced with the question of authority a lot lately. I feel God's call to serve Him in ways that my parents are reluctant (to say the least) to allow. Being 18, am I out from under their authority? I honestly don't think I ever will be, and I'm okay with that, but sometimes I feel like I have to decide who has more authority- my parents or God. Which God obviously does, but how do I disobey my parents to obey God when He says honor your father and mother?