@TotallyAbsurd
Honestly, I would say the writer knows more than you're criticizing him for. He has had to let go of his pacifist ways and kill a person in order to protect those he cares about, even needing to be more proactive to ensure wars don't get out of hand. I can also see the 500 years of living a laid back life having an effect on his perception of time, both helping him remain sane living that long but still hindering his ability to live alongside "short live'd species."
But when I think about the "childish way he acts", I see a lot of similarities with Uncle Iroh from Avatar, that he's sitting back and enjoying life during his travels instead of worrying about the little things that can distract you from the joys of living.