what should be the rating for a 9 year old?
My honest opinion? Don’t focus on what it “should” be. If you play enough, (and learn enough), your rating should rise to your skill level.
I'm Nine and 859 USCF is that good?
I've seen worse. But remember, no one expects a 9 year-old to be able to play like a GM.
Ratings aren't based on age but age can help with performance kids can learn better than adults sometimes
Don't worry about it just focus on improving whatever you want to improve at