Who Are Young Adults?

"The Young Adult Library Services Association (YALSA) of the American Library Association (ALA) defines young adults as youth aged 12 through 18" (2008, Chance).  When contemplating the question of who are young adults, my first thoughts were 12-18 year olds.  I still go by this idea, but I think that the lines of definition are blurry.  The typical 18 year old high school graduate would want, by his own definition, to be defined an adult, and the typical 10-12 year old middle school student, especially the girls, would probably want to be thought of as pre-teen and not a child.  In reality, the answer probably truly lies with the person who is answering the question at the time; however, I do think that by focusing mainly 12-18 year olds, we can probably focus on most interests of young adults.