It's not uncommon in sports. That's the kind of thing I'd expect to hear in the locker room or on the ice when playing hockey. I don't feel like maturity plays into it there. It's almost a term of endearment.
Yes, I am aware. But then again I phrased my original statement to show that there was a small frequency of use of these terms. Where females (in my area) have a very high frequency of referring to each other as girls. Almost like "woman" is a formal term.
those _are_ boys.