I've been thinking about this today and wondering what impact it has on how we view both women and girls. Does it assist the blurring of the age of consent? Or how we reduce women's value by talking about them as children.
I think you could talk about a "girls' weekend" in the same tone of voice as a "boys' weekend". But the lack of any female equivalent to blokes, guys, chaps, fellows seems to say something about how we think about women versus men. And it's not that having informal ways to refer to people is either elevating them or demeaning them--it's just that we're used to talking about men in a neutral way. And somehow when we want to do the same about women, we haven't got the language.