My son went through something similar when he turned 18 and I found it terribly frustrating. I didn't want to push him out of the house but after a few months I finally snapped. It may have been less time but to me it seemed like an eternity.

I told him that if he wanted to be treated as an adult then he needed to behave like that and not a spoiled teenage who feels like they have power. I explained that if he lived with a friend, he would show them more consideration. So we set a few rules that he felt were fair and we allowed him to a few things he felt would mark him as an adult.

Hope that helps,
Mona