If I'm not mistaken here in NY school is mandatory to age 16. That means if you decide to leave school at 16 you can do so but you will not have earned a HS diploma, unless you have already earned all the credits necessary to obtain one.
I knew plenty of kids who graduated at 16 by taking all the credit courses and completing the graduation requirements. I also knew plenty who just dropped out and then went on to a business school or trade school and there completed a GED program (General Equivalence Diploma).
Believe it or not, there was an elder in my congregation who was encouraging me to drop out at 16 and go to the business school that his wife went to. I went and met with the school's admissions director. He was appalled by that elder's idea and he strongly urged me to stay in HS and go on to college.
Good thing I listened to the school director and not the elder!