I think that a case can be made for Amir being the most emotionally mature. Amir is the character that must set out to be "good agin." In this very motivation of restoration lies a maturity that understands the need to make what is into what should be. It is this maturation that enables him to go back to Afghanistan, seek out confirmation as to what happened to Ali, and also understand that his journey and quest might revolve around someone or something larger than him. This becomes Sohrab's well being. Amir matures the most in my mind because of this reality. He is one who understands that, on some level, his journey is not about him as much as it is about Sohrab and how this opportunity is representative of how Amir should have treated Ali. When Sohrab attempts suicide, Amir falls to his knees and prays for the first time, indicating a submission of self that had not been a part of his character prior. This shows a maturation and development of self in how he is able to put aside his own sense of identity for embracing someone else's. The fact that he becomes Sohrab's kite runner, is also representative of his maturation throughout the narrative.