Sure, Billy ages 2 years over the novel, but most of that takes place in the first 3 chapters. His real coming of age starts happening once he's got those cute little puppies in his hot little hands—er, gunnysack.
Billy goes from being a 10-year-old boy obsessed with hounds to being 12 years old and having experienced sacrifice and death. You don't go through that sort of emotional roller coaster without growing up a bit in the process. This emotional maturity is what constitutes a coming-of-age story. By the end, Billy is ready to move forward into adulthood. We mean this both figuratively and literally, as his family is moving.
The narrator really drives it home for us when Papa tells Billy that the family was going to leave Billy behind and let him stay with Grandpa so he wouldn't have to leave his dogs. But that would have left Billy in a state of idyllic childhood, when in fact it's time for him to experience loss and suffering—and grow up.
Yeah. That's the thing about growing up: it's not all driver's licenses and midnight curfews. Sometimes it's watching your beloved dogs die and leaving behind your childhood home. Kind of a bummer, right?
There's nary a pirate nor errant knight to be found in this book. So what's so adventurous about it?
Well, we do get a whole lot of life and death situations. A boy running around in the woods with his dogs is bound to have a few adventures. And if danger, heroism, bloody battles, and sacrifice don't qualify a book as an adventure story, then we might as well hang up our sword right now.
Though we at Shmoop firmly believe Young Adult literature doesn't have to be confined to just young adults, this book was clearly written with that audience in mind. We've got a young narrator and protagonist telling his story. He is constantly giving us his opinions, thoughts, and perspectives. He's totally relatable to the young adult crowd. And even though Billy is a very mature 12-year-old, this book is still firmly in the Young Adult genre.