Why is the "coming-of-age" theme so significant in "Other voices, Other Rooms"?

In Other Voices, Other Rooms a major theme is coming of age. When Joel leaves New Orleans for Skully's Landing, he is essentially a child, but at the novel's end, he senses his own maturation and looks back with detachment on the child he used to be. Finally he can acknowledge the sexual attraction he feels for Randolph. Moreover, he realizes that his is the stronger personality and that only he can provide the reassurance Randolph needs —that everything will be all right.