Wait, what? What places have older kids start school earlier? Why would you do that?
Almost every 7 year old I've ever known naturally woke up at the crack of dawn. Almost every 16 year old I've ever known would sleep till noon if you let them.
My school district had older kids start school later (7:45 for elementary, 8:30 for middle, 9:15 for high), and that seems fairly sensible.
There is a surprisingly persistent belief that waking up (and going to bed) early is more moral. That it's somehow related to responsibility, work ethic, strength of character, etc.
Proposals to start school later are often dismissed on the basis that students are just whining about the character-building that they ought to be subjected to.
Staying out late and sleeping in are both signifiers of irresponsibility/laziness and things that parents and parent-like figures discourage. Despite the fact that, so long as you are doing both at the same time, you're still getting adequate sleep and probably just as healthy (if not healthier).
Fairfax apparently recently changed (or will change) for high school to start at 8 am. That's still earlier than I think is civilized, but it's an improvement. (One that I would have welcomed as a high school student.)