I'll never get over how they always separate the boys from the girls in PE classes. Like, even if girls enter puberty earlier than boys on average, they're all going through puberty at different rates. The playing ground isn't even regardless, separating on gender is going to do diddly squat if you're looking for balance/fairness.
Hell, even if one group had some obvious advantage over the other, all you'd have to do is balance the teams so it's not all boys vs all girls or something.