Why should school start later for teens?

I think  school should started time later. Many people live far from the school. Example for myself, I can't be late for 7:30 when I was in high school. I got up at 6 o'clock every day. The get bus for twenty minutes to go to school for classes. Although this traffic time is not long, the buses in the early morning are not as late as early, so I think it can be gain to get more sleep.