Your daughter is precious!
I teach 7th grade and I think that is not logical thinking. As a parent, I dont want my girls in class with boys 2 years older either. But I am not going to hold them back academically so they can be older and bigger in their class.
My suggestion: if you are in a school system that you are uncomfortable with, try a private school. Sure its a huge sacrifice, but your children will not be exposed to and expected to tolerate all the mess that exists in some public schools. I know because I have taught in both.
Speaking as a teacher, please dont hold your daughter back for the reasons you listed. If the boys are 2 and 1/2 years older than her in one grade, dont you think there will be some like that in the next grade too? Thats not the way to escape it. I see children who were held back and they often resent it if they didnt need it. They are made fun of as well.