You want a quick way to gain some maturity? Get yourself a pet. And then wait for it to die. Yeah, nothing makes you grow up like some responsibility and tragedy. In Where the Red Fern Grows, Billy does a whole lot of growing up once he gets his dogs. He trains them, cares for them, and certainly learns from them. Eventually he even uses them to bring in money for the family, which gives him more responsibility as a family breadwinner. This isn't just a book about two dogs and a boy; it's about two dogs turning a boy into a man.
In order for Billy to mature fully, he must experience the loss of his hounds.
Billy's transformation to adulthood doesn't begin until he starts hunting. Until then he is still immature.