Most young adult novels are over 30,000 words long or 120-250 pages. Although younger adult novels can deal with intense and serious subjects, they are often mysteries and thrillers--stories engrossing enough to appeal to younger kids as well as older ones. The older young adult novels deal with more complex subjects.
What distinguishes a young adult novel from an adult novel is often nothing more than subject matter. These books are complicated, sophisticated and challenging. They are not limited in what issues can be discussed, nor are they in any way "kids' books." By this age level, there is a high tolerance for ambivalence in both character and plot, as well as a general acceptance of complex and painful subjects.
Nancy Lamb, Crafting Stories for Children, 2001