I have three brothers and no sisters. My parents have 11 grandchildren -- nine are boys. My H has one twin brother. Girls are few and far between on both sides.
It seems like the board seems to have a little over 50% girls on average. I think I've read this is normal for older moms - this was the first hit I got on the topic:
Interesting. Although in my small social circle of parents, I'm the only one that meets that theory. All the girl mom's were younger than me when our kids were born (I was 27) and all the boy mom's are older.