No, you are not a legal adult anywhere in the U.S. until you are 18 or are legally emancipated, which means you are treated just as if you were 18 years old. If you will be residing with someone in a stable home who is taking on the economic and legal responsibilities associated with you, then that person needs to have legal guardianship over you, and/or you would need to become emancipated. It is about legal status - not having enough money to support yourself.
If you do nothing (legally) and simply leave your parents or current legal guardians, you are considered a runaway, and anyone you are living with can be charged with aiding and abetting a runaway. You should not put someone in that position.
There is a high standard you must meet to have the court grant your petition for emancipation, and you should have an attorney assist you, or you are almost guaranteed having the petition denied.
I would suggest contacting a lawyer to discuss the specific facts of your situation and your legal options.
