How did Jem's behavior toward Scout show his growing maturity?

Scout cries that night and Jem consoles her. 

"Try to go to sleep," he said, "It'll be all over after tomorrow, maybe.... The full meaning of the night's events hit me and I began crying. Jem wasawfully nice about it: for once he didn't remind me that people nearly nine years old didn't do things like that." 

Jem is seeing his sister as a person that needs the comfort of her big brother rathar than simply his little sister who pesters him.