I believe it is 18 but most teens leave around 16-18 cause of problems like fights with parents or don't have enough money. Ect... But it also depends on what state you live in. You can look it up online for you state.
There is no legal age limit that is set for a child to leave home. Some say that at 18 a child should have leave home but it is not recommended. Parents are however advised to relax their governance on children at the after of 13 and let the child decides when to leave home.