The only way to accelerate grades is if one of your teachers notices that you are well above average. You can't just be put ahead, and then if this is only one teach you may only be put ahead in that one subject.
You may be considered to be accelerated if you are a good student, can easily handle the work, are getting great marks and teachers think you are emotionally and academically capable to handle accelerated learning.
So basically the teachers deal with who is put ahead and who stays behind. If you want you could discuss it with a teacher if you think you are competent enough however if i was you i would stay where you are.
Im not saying this on behalf of all accelerants, but from my own experience it can be a challenge. Remember when all your friends are out drinking and going to clubs, you wont be able to, and you will be left out of a few things. I did get around and still are getting around some of these age limit issues, however bars and clubs are off limits unfortunately.
There are upsides, however it depends how much your willing to give up. I was waiting for my mother to pick me up from school the other day when i saw somebody in year 10 drive off with their L plates, while i still had to climb into the passenger seat.
Also when all my friends decided to go out, or go somewhere where driving as involved, i was limited,i either had to rely on friends or my parents, and still do. So i will stop rambling now and let you decide what you want, but remember its not all fun and games being years ahead of what you should be.