I'm a 13 year old girl and share a room with my 9 year old sister. Our mom always sends us to bed at 8:30pm, although I'm 4 year older. My sister is nagging that she can't sleep alone. 8:30 pm is too early for a 13 year old, I think. I should stay up later, I suppose?
I'm going to interpret the question as asking how a parent can manage the bedtimes of siblings of different ages, as I think that's a great question, and answerable (as opposed to asking for an opinion).
I have two children, and not only are they of different ages (though closer, a year and a half apart), but the younger one naturally needs more sleep than the older even age-for-age. What's more, the younger one wants to sleep with the older one (in the same bedroom, often!), and definitely wants to go to sleep at the same time - it is "unfair" if the older one goes later, and on top of that it's just impractical given they (voluntarily, on both parts) share a room.
There's issues here on both sides, that I think can be balanced - but you have to understand them both. For the younger, it seems unfair that the older child should go to bed later, even though they probably do need a little less sleep. For the older, it is unfair to have to go to bed at the same time as a much younger child when all of their friends are going to bed later.
How we work on this is twofold. First, we do technically have "different" bedtimes de jure, though they aren't different de facto - meaning, officially the younger has lights off at 8:30pm and the older has lights off at 9:00pm, but realistically they both go to bed at the same time. Lights off for us means the e-readers turn off at that time; but we allow the younger to extend his time to 9 if he asks politely. This is not just us being "say please before we do something" - it's actually a test: is he overtired? If he is, then he won't be able to ask politely.
Second, we allow them to wake up when they want - and so the older one wakes up earlier. If he really is getting enough sleep, then he'll wake up on his own earlier - and then we allow him to do "fun" things in the morning, once he's gotten ready for school. Wake up, get dressed, make lunch, do morning chores, and get breakfast; after that's done, he's allowed to play on his screens until a little while before school. That "makes up" for the perhaps slightly earlier bedtime - because he wouldn't be allowed to play games that late in the day anyway.
I suspect as a kid this answer doesn't really hit all of the points you'd hope for, but I would encourage you to think of things from both sides here - it will help you make your case for change. Balancing things like this, when both kids have a reasonable argument, is hard - both for parents and, well, everyone else. Having kids go to bed at different times who share a room is very difficult, because bedtime is the time where you have the least self control. This is true for adults, also - ask anyone who's trying to lose weight when they're most likely to have snacks, the answer is probably late at night. So your younger sister will have a much harder time being reasonable, even if it is entirely reasonable to tell her that she just has to go to bed earlier, just because it's late and it's hard to think rationally when you're tired! So, parents have to find compromises - and sometimes the compromise is something nobody really wants. (That's how you can tell it's a good compromise - if nobody's happy...)
The key to finding a solution that does make you happy, if the above answer doesn't work for you or your parents, is finding something that will actually work, and making the suggestion for how to make it work - and making sure it works for both parties. Not just it "should" be fair, but that your sister actually thinks it is fair and is willing to do it. If you want to go to bed an hour later, what can you do to help your sister feel that it's fair? Find out what she wants, and see if you can come up with something that works - and that isn't going to require more work from your parents. Parents (and anyone in charge of anything) tend to be very positive about changes that don't require them to listen to complaining or do anything extra!
Teens should get between 8-10 hours of sleep a night. Since you are at the young end of that range, you should err on the side of needing closer to 10 hours
So 8:30 is a little early for you, unless you are waking up at 6:30 in the morning. FWIW, it might be a little early for your sister too.
A 9 year old does not need you to fall asleep. Though you might compromise by changing for bed and brushing your teeth when she does, so you don't wake her up when you go to bed.