The exact same thing happened to me in my school concert band last year. I was in year 10, and this other girl was in year 12. I was alot better than her, but since she was in year 12 she was put on 1st and I was put on 2nd. I found it really unfair, but in the end there's nothing you can do about it, just play the part you were put on as best you can.
And just remember, the time will come when you're in an older grade and will be given preference
