Unfortunately teenager and adult hours are forced to be synchronised, so schools just cannot open later.
No, they aren’t. Even with the progressive infantilization of children over the last several decades, its still generally widely accepted that children over 12 can be left alone for a few hours at a time.
Though shifting the standard workweek to 30 hours and adjusting to that by moving the standard start time forward by two hours wouldn’t be a bad idea, either.