At 14 years of age the 14 year old needs a minimum of 9 hours of sleep to function properly the next day.
So if you need to get up at 7:00 AM to get ready for school then 14 year old should should go to bed at 10:00 PM so they can get 9 hours of sleep.
Of course the more sleep you get the better off you'll be so if possible get into bed by 9:00 PM to be up by 7:00 AM so you can get enough sleep and have time to fall asleep.
But you should be in bed by 10:00 PM at the latest and no longer than 11:00 PM for the longest amount of sleep.
As long as the 14 year old is getting 9 hours of sleep they should be just fine but the more sleep the better.