It's because teen boy skins were made first and just called teen skins. Then came along girls who kept making the same type of skin repetitively, and people called them teen girl skins. Also teen boy skins are different to teen girl skin.

Really, what kind of question is this?

There are many different kinds of skins, and if a skin happens to resembe a male person in his teenager-years, of course it's called a teen boy skin. Why wouldn't it?

The thing is, skins of male teenagers usually are crappy and copies. However, there are a lot of users posting female teenager-skins that are much higher in quality and mostly original content. That's why the term "teenager girl skins" so popular, while "teenage boy skins" isn't as much.

Also, not every girl skin is a "teenage girl skin". What in the world would make you think that? Same goes with boys, heck, there are even skins that are neither male nor female...

lol, Good Question.

Baby boy skins* ^^ THAT POST BEFORE WAS MY 100TH. KTHX

I don't think so... They're called Teen Girl Skins, not just Teen Skins. Often times there's little girl skins too though, nobody usually makes baby girl skins.

It would be much easier to answer if you gave some examples.