My only "pre-existing notion" of a young Kirk is, I guess, a young Shatner, circa "Judgement at Nuremburg" or "The Brothers Karamazov".
As I recall, Pine got decent reviews for "Smokin' Aces" so he might work out as the young Kirk. Still, of all the actors, I think he has the biggest hurdles to overcome since Kirk is so tied to Shatner and, unlike Spock, you don't have makeup to help with the casting.
