A 14 year old should get around 10 to 11 hours of sleep so the time they should go to bed depends on how early they should be up.
But most 14 year olds should be in bed by 9:00 PM to 10:00 PM at the latest so they have enough time to fall asleep and get enough sleep before they wake up.
I used to go to bed by 9:00 PM when I was 13 and 14 years old and the older I got I started staying up till 10:00 PM to 11:00 PM.
As long as the 14 year old is getting at least 10 hours of sleep or even 9 hours they should be fine but it's best to get plenty of rest so that you can function during the day and have better health.
Being sleep deprived is bad for your health but getting enough sleep can keep you healthy.