Ok I agree with hawaii Gymnast - How can you have as you posted high 8's and low 9's in competitions if you never competed? It can't be both ways.
You have also posted you have had ALOT of sickness and injury which could mean that although you are doing certain skills the are now weak and not as strong as you need to build on for the upper levels. You can't move up on skills you haven't done in a while because of sickness or what ever. Optional levels builds on having very strong skills from the level before. You need to trust that your coach has the ability to evaluate every gymnast and choose the road that will be the best for every gymnast.
YOUR gym may have younger girls only at this level but if you go to meets you will see there are alot of girls at this level at your age, just not at your gym.
Coaches don't make decisions on moving kids up, down or whatever to "punish" gymnasits. They choose where you should be based on the skills you present, how well you listen, how well you are a team player, how your health is, how your recovery is, how well you are focusing on you and not worried about others gymnastics and basicly what is the route that will be best for you and your gynastics.
The truth is that some will advance quicker than others and when there is alot of injury and sickness as you have claimed you sometimes have to go back to the basics to clean up those skills, gain strength, and show the coaches you are focused on YOUR gymnastics and will give them 100% +. Your coaches have probably spent many hours thinking for every gymnast what is best for each of you.
If you don't like their decisions then you can quit the sport, go to another gym and be evaluated and possibly go to their team, or suck it up, stop complaining about what everyone else received and what you didn't get and show your coach how good a gymnast you are.