It was certainly a factor, but I don't know that it was a boy vs. girl thing as much as it was the fact that he was a tiny kid. Even redshirting him, he's still on the small end of his class.
And at the end of the day, even if I wish it weren't true, things like size and maturity can have a big impact on a child's experience in school, especially when it comes to boys. To us, it felt like it was a way for us to give him the best chance at success and happiness.
Also to @simply1 's point - yes, our son had ADHD that hadn't yet been diagnosed, and was far too active to just be turning 5 the first day of kindergarten. He also had big emotions, and letting him do Early-K allowed those to moderate, him to grow, and him to settle down (a little, I guess).
