A child must either reach the age of majority, which is over 17, or have a parents' permission to move out of the house according to Cornell University. Eighteen is the age of a legal adult in the United States.
The age of majority is different around the world. In the U.S. the general age of majority is 18; however, Puerto Rico and Mississippi have raised the age to 21, while Nebraska and Alabama have set it at 19.
If a child is not of this age and parents do not consent, one does have alternatives. The hardest option is to file for emancipation in a state court. For this, the child must prove financial independence, housing options and maturity. Getting married would achieve emancipation, but a youth must have his/her parents' permission to do this before the age of majority. Enlisting in the military is another option.