Student Exchange Programs

Hey there. I am 15 years old and currently live in England. If I was to go to America, NC on a foreign exchange student program, how long would I be able to go for? This is mainly because I want to go and see my girlfriend who lives in NC but I have always dreamed of living in America. I would like to know how long I would be able to go over there for. However, how long could she come to England for from NC, America? We want to do one or the other so we can see each other frequently. So how long would I be able to go over there for and how long would she able to come over here for? Everybody who has taken their time to read this and answer everything I have said, it would be much appreciated. Thankyou! (: