I have no clue who came up with this, and I'm sure you've seen it several times before, that YA is referred to as a genre. Well, it's not!
Young Adult fiction, often abbreviated as YA, is fiction written for, published for, or marketed to adolescents and young adults, roughly ages 14 to 21. The exact age group certainly isn't set in stone as YA is sometimes defined as "between the ages of 12 and 18", "texts written for the ages of 12 and up" or "literature written for ages ranging from 10 years up to the age of 20". Another suggestion for the definition is that Young Adult literature is any text being read by adolescents, though this definition is somewhat controversial especially considering the fact that many adults will read books that are viewed as YA as well. But maybe this just gives new meaning to being young at heart!
Although YA literature shares the fundamental elements of character, plot, setting, theme, and style common to adult fiction, theme and style may be subordinated to the more tangible basic narrative elements such as plot, setting, and character. The vast majority of YA stories portray an adolescent as the protagonist, rather than an adult or a child. Themes in YA stories often focus on the challenges of youth, so much so that the entire age category is sometimes referred to as problem novels or coming of age novels. The subject matter and story lines are typically consistent with the age and experience of the main character, but beyond that YA stories span the entire spectrum of fiction genres, from contemporary straight to science fiction. Writing styles of YA stories also range widely, from the richness of literary style to the clarity and speed of the plain and unobtrusive.
YA isn't a new phenomenon, instead a classification that only received its name in the past decades. Examples of novels that predate this classification, but that are now frequently presented alongside YA novels, are Anne of Green Gables (Lucy Maud Montgomery) or Lord of the Flies (William Golding).
And to get back to the beginning, let me repeat that Young Adult is not a genre! I cannot stress this enough! It is ... wait for it ... a category defined by the reading age/level! Fantasy is a genre. Horror is a genre. A whole lot of things are a genre, but YA isn't one of them. 'nuff said.