In Star Trek 09, Spock Prime is startled that Kirk is not the captain of the Enterprise yet. Spock Prime expects Kirk to already be the captain, though it is obvious from his appearance that he is much younger than he was in TOS, so even if Spock isn't quite sure of the date, he would at least recognize Kirk's youth, we can assume... and the film is canon, unlike those earlier works (novels, comics, etc.). Could this means Kirk assumed command of the Enterprise in the prime universe much younger that originally portrayed in other fiction sources, and several years prior to the 5 year mission? Perhaps he assumed command shortly after the Farragut incident of 2257, for some reason? The film also establishes that in the Prime Universe, Kirk's dad lived to watch him become Captain of the Enterprise, which also contradicts the earlier novels.