Have you tried talking it over with them? Showing them how mature you are can be a great starting point to them treating you more like an adult. Maybe you could try constructing an argument - work out what point you want to make, and think of +s and -s - just to show that you have thought it out and rationalised it in a mature way. For example:
Proposition: "I'd like to have more flexibility sometimes with my bedtime"
Provisos:
- If I'm tired, I take full responsibility.
- It will only be in exceptional circumstances, rather than the norm.
- If I have one later night, I will follow that by an earlier night.
Considerations:
+ I sometimes cannot get my work done by the time my bedtime comes around, and so I end up staying up later and doing the work, or not completing it as well as I could do.
+ By giving me some responsibility in choosing my own bedtime, it's empowering me to make my own choices and identify what is better for my body in terms of sleeping times.
+ Sometimes social events interfere with getting to bed at the specific time, which means that I end up missing out on seeing friends or developing a social life.
- It is useful having a standard time to go to bed.
- It is more likely that I would be tired if I go to bed later.
- I am more productive if I have a better sleep.
etc. etc. - sometimes parents don't realise how mature their children are, so showing that them you've considered and weighted up the options may work in your favour. It may not do too, of course :P But it's my suggestion.
In fairness, a lot of people I know go to bed at a pretty standard time anyway, so it's not as though that's any different. But I do understand that it must suck sometimes!
Good luck, anyway.