You choose bedtime
Parent/Guardian chooses budtime
Starting in the 9th grade, though
I feel as if you should be able to choose it yourself growing up as long as it's sensible, if not parents step in. As no young children are really sensible about their bedtime it would always be parents.
When your younger you don't normally know what best for you, when you get a little older i see why you would want to stay up later but still don't know what you really need
If I was allowed to choose my bedtime I would've never slept. Parents (most of the time) know what is best for their child because they have had more experience.