Young people certainly have their coming-of-age novels, but the narrators of those books don’t present the stories as if they’re investigating why and how the heroes became the adults they are, which is a quality of bildungsroman novels (think David Copperfield). Young adult novels have a more in-the-now feel, with the main characters’ maturation usually taking place within a short time frame, such as a single year of school. Rarely do they cover a full childhood or young adulthood as Dickens does in his classic. Novels featuring longer maturation windows can still be for kids if their narratives have a youthful sensibility. That sensibility is arguably the biggest marker of a young adult book. Adults are already self-aware and consider why they and others behave as they do (even if they don’t always exercise that mature perspective!); adult novels with this mature sensibility are not “young adult books” even when they feature young heroes. In contrast, young people are just starting to shed their self-centric perspectives and tend to judge and act without first considering how their actions will affect others. The heroes of their novels may reach a higher level of self-awareness by the end of their novels, but they don’t start out that way and their narratives reflect that. So, when you’re considering whether a story is “for” adults or children, weigh its narrative sensibility.