How can it be Kakashi? Naruto's dream from the very first chapter was to become hokage, and that's what he kept on babbling about all this time. You really think Kishi's going to abandon the main character's hopes and dreams and give the hokage spot to Kakashi? With Naruto coming to an end (the war being one of the final arcs), there is no room for Kakashi to become hokage. Age doesn't matter, Gaara became the hokage at 15-16. Besides, Naruto's going to witness the death of his friends, and he now realises what's at stake. I think he'll mature by the end of the war.