How is Ponyboy shown to be immature at the beginning of The Outsiders?
Ponyboy is unaware of the real pressures on those around him at the beginning of the novel. He feels that his older brother, Darry, doesn't understand him and is too hard on him. It is only by the end of the story that he realises that Darry has a constant fear for his brothers' welfare after the death of their parents, and he has given up his own potential success to support and nurture similar skills in Ponyboy.
Ponyboy does not appreciate the danger that isolation can bring. Although he is aware of the attack on Johnny, he goes to the cinema alone in Chapter 1 and is jumped by the Soc's. He has always been protected by the members of the gang and his family, and has to learn the value of this support.
Ponyboy summarises his understanding of his brothers in chapter 1-
Darry's gone through a lot in his twenty years, grown up too fast. Sodapop'll never grow up at all. I don't know which way's the best. I'll find out one of these days.
In the course of the novel he goes some way to tackling this question. He also finds out that Soda did indeed have grown up responsibilities as he had proposed to Sandy and believed he was to be a father. Ponyboy ultimately has to learn to look outside himself in order to mature.