I don't think a 60/40 split is anything to worry about. Remember that in any given school, you aren't looking at a very big sample size, population-wise, so it is to be expected that the numbers of kids of each gender might be a bit "lumpy". If the numbers were perfectly balanced, I might suspect that some qualified kids were being denied services or that the cutoffs were being massaged in the name of gender equality, which would worry me a great deal more. I grew up the only girl in a family with five brothers, and most of my friends growing up were boys, and it doesn't appear to have damaged me in any way.