I read a very informative and interesting article in National Geographic about sleep ( I think about 2 years ago). Teenagers can and sometimes should sleep bettween 10-12 hours a night. These are important growing years (we think they are lazy). Try Google this article or the studies that have made about this.
It really depends on the child my son is 14 if he sleeps more then 5 hours a night so he goes to bed between 12:30 and 1 a.m. If he sleeps more he is sleepy all day. I have always been that way all my life. He is healthy very active and an honnar student.