I wish someone other than me had read Diane Carey's "Best Destiny" which is what Orci and Kurtzman referenced as one of the inspirations of the new movie's story.
In the novel, Kirk is a 16 yr old hellion, ticked off at the world because he had to live through the Tarsus 4 massacre and his dad is never around- always off on Starfleet missions. His dad forces him to come with him on a cruise with Capt April on the Enterprise, a milk run where Jimmy won't get hurt but might learn to expand his perspective about the world. The first half of the book Kirk spends much of the time rebellious and sullen, but when pirates attack their shuttlecraft, he starts to slowly begin to realize his problems are incosequential. The essential lesson that a hero learns when they realize their place in the grand scheme of things - that the world doesn't owe you, you owe the world- gets through to him and he starts to become the Kirk we all know. I also think the last few pages of the book offer a little more insight into the character - in one passage Capt April explains why he agreed to diverting his mission so Jimmy could get this milk run and hopefully become a responsible person. April says that Jimmy's rebellious/troublemaking spirit is central to what is required for Starfleet because "you can't fight a dirty soul with a clean one"
I gather that when the timeline is changed, George Kirk will never be able to teach his kid this lesson, and that Kirk will remain a hellion for a lot longer, getting into fights, bedding women, breaking rules etc. I also guess that Pike will be the father figure here, offering direction and faith in him until he gets to be the Kirk we know. It's interesting, to echo that dirty soul vs clean soul comment in the book by Capt April, that the Capt Pike dossier on the official site states that he was tired of Starfleet picking by the book commanders, he wants someone with original thinking to lead Starfleet.
"Best Destiny" is out of print BTW.