Quote Originally Posted by Mercen-X
I think the point of "G.U." is to act as a reference to those terms rather than actually being the initials of any specific title.

Perhaps G.U. part 1 is made up of five chapters and each of those phrases is the title of those respective chapters.
http://ps2.ign.com/articles/622/622135p1.html
Yeah they seem confident to say its "grow up" as opposed to one of those other GU titles as growing up is the main theme of the game.