What are some examples of how Jem grows up too quickly?

Consider chapter 23. In Chapter 23, Jem is trying to make sense of everything that has happened. Jem tries to comfort Scout by explaining that Aunt Alexandra is just trying to make her into "a lady." He says that there are four different kinds of people in Maycomb county: "ordinary" people like themselves, people like the Cunninghams in the woods, people like the Ewells by the dump, and black people. Each class looks down upon and despises the class below it. The two try to resolve exactly what separates and distinguishes the categories of white people. Background doesn't seem to matter, because all the families are equally old. Jem thinks these class definitions have to do with how long the family has been literate. Scout disagrees and thinks, "there's just one kind of folks. Folks." Jem says he used to think so as well, but he doesn't understand why they despise one another if that's the case. Jem seems very frustrated with society, and adds that maybe Boo Radley stays inside because he wants to. Jem hs certainly matured since the beginning of the book. Earlier in the book, Jem was concerned with playing games and trying to lure Boo Radley out of his house.