Young adult (YA), new adult, middle-grade, and early reader are all what we call addon genres, in that they mostly only exist when added on to another genre: YA thriller, middle-grade fantasy, etc. They are also defined entirely by the age group of their readers, though there are style, plot, and theme considerations for each group. The age ranges are: 5 – 8 — Early reader 8 – 12 — Middle Grade 12 – 18 — Young Adult 18 – 25 — New Adult Books obviously get longer as the readership gets older. The guidelines for book length in trad…