Well... when girls are told they can do anything boys can do, I don't think it includes zipping down their flies and peeing in the toilet standing up. The phrase has come to refer to goals, talents, hobbies, and behavioral strengths. I'm just considering the reverse as food for thought. (And if you want to get technical, people biologically born as men could get boobs and even experience menstrual symptoms, if not cycles.. but that's beyond the scope of the point I'm trying to make here!)