Growing old is gracefully (or not) accepting the passage of time. Generally speaking, you have no choice.
Growing up is being slapped in the face with the understanding that you must be the hero you have been waiting on your entire life.
Growing up and growing old - there's a difference, but both will break your heart.
For those of you who don't know me well, three of my favorite movies are Treasure Planet, Atlantis: The Lost Empire, and How to Train Your Dragon. The movies are very different in plot, so it took me a long time to figure out why I loved them so much (especially when I consider myself a bit old for most animated movies). I realized that the common thread is that, in each of these movies, the protagonists were looking for approval and a hero in those around one, and not finding one. So they decided to become their own hero. It was never really a conscious decision, but more of being pushed to the point in life where they realized that no one was going to save them and what they loved; they were going to have to fight for it. Having recently been pushed to that point in life, I understand and love these movies all the more. Rant over.