In chapter 5, Scout talks to Miss Maudie about Boo Radley. Scout asks Miss Maudie why Boo Radley doesn't want to come out of his house. Maudie's response is to tell Scout that Boo Radley's father was a "foot-washing Baptist" (44). She explains Boo's father was very strict and believed anything pleasurable was a sin. Also, from what Miss Maudie remembers about Boo Radley, he was a nice when he was a boy.
Jem and Scout also learn a few things about Boo when they receive gifts from him in the knothole of the Radley's oak tree. They find a spelling bee medal that he must have earned in school when he was a boy. They also learn Boo likes shiny pennies, old watches, and carving characters in soap. Based on all of this information, Boo Radley seems normal and innocent enough to live a regular life. Boo's mean father seems to be what prevented him from that life.
Things changed for Boo Radley when he got mixed up with the wrong crowd in high school. He got into a little trouble with the law and his father condemned him to a life of house arrest because of the embarrassment. A few years later, when he was in his thirties, Boo stabbed his father with scissors, causing him to be in trouble with the law again. Boo Radley's childhood did have some aspects of normalcy, though, because he did go to public school and participated in activities like spelling bees and soap carving.