Take it from someone who frequents a college campus, guys being immature in their twenties is nothing new nor special. On the other hand, I see just as many women acting with the same amount of immaturity as I do guys. They tend to just go about it and express it in different ways. I still hold to the theory that people in general, not males, not females, have a difficult time “growing up.”
If their little games of pretend bother you, tell them that and don’t play along with it.