First, The books came first. This means that the movies needed to follow what the books said. Second, They combined the last four books into the second movie. Yes, There was a second movie, And no, It was not better. It's like they glanced at the books and only kept one thing per book. Finally, The creators of the movie aged everyone up, Despite what Rick Riordan said. I mean, They were supposed to be young! It was part of the prophecy, Which was the center of the books.