I skipped a grade and my mom told me that the school district really didn't like doing it, for many of the reasons you mention. She said they did it with me because I was also large (I think I was even one of the biggest kids one grade up) and mature (a characteristic which seems to have flamed out early). I don't think I suffered many ill effects. One thing I did notice in retrospect, seriously disadvantaged in dating

I also have 3 brothers and agree with the ability to fight and get along. People who can't argue about stuff without becoming enemies...I just don't get them