My brother is 18 years old, and he reads all varieties of books. I daresay he does prefer male protagonists, but I don’t blame him, because I prefer female protagonists (but certainly do NOT limit my reading to that – male protagonists can be wonderful, too; I just relate to girls better). However he has no qualms about reading and talking to friends about books with female protagonists, too. For instance, he recently read DRAGON’S KEEP by Janet Lee Carey, which he enjoyed, although not as much as I did. Whereas he LOVED Carey’s BEAST OF NOOR, with equal parts male and female protagonists, but which I did not love so much.
I’m not sure this really helps to answer your question, but I thought I’d pitch in anyway. Even if girls might prefer reading about girls, and boys about boys, I do not believe either sex necessarily limits themselves to what they read because of the book’s main character’s gender.
I have loved books with boys featured prominently, my brother has loved books with girls feature prominently. And that’s that.