>>3488924>he doesn't look, talk or act(mostly) like a 14 year oldI mean, he gained universal knowledge by sacrificing his leg and the main theme of the manga is the loss of his innocence and the end of his childhood.
I think there's mentioned at some point in the manga that people don't make it out alive or sane after they see the door of truth and that's why the brothers are so important to the overall plot (and the reason Bradley was so lax with him when he recruits him)
