How is Holden heroic and how is he different?
Holden is both a hero and someone who walks to the beat of a different drum. He is heroic in the sense that he rejects the norms of society, the expectations of his parents, of his teachers, of his peers, because he has found a fatal flaw in society.
He has a question that no one can answer. How can a world allow a young boy, Holden's brother, Allie, to die without having a chance to experience life? No one addresses this question, because Holden does not ask it. He keeps it locked inside his heart and mind and it torments him. He is stuck in a circle of grief over the death of his brother and the fact that everyone has returned to life as normal disturbs him. For Holden nothing can ever be normal again.
Holden looks at life differently, he is unhappy with the rituals of teenage life. He rejects the idea of friendship, never acts on his attraction to Jane Gallagher, he just get jealous when Stradlater dates her. He dates Sally Hayes, but he insults her. His behavior is erratic, he lies, he makes rash decisions, he sneaks around hiding from his parents in New York City.
Holden is in pain thorughout the book. It is clear, that he needs to be in the mental institution that he tells his story from at the start of the book.