Easy is part of an emerging subgenre called “New Adult” literature. NA books are appropriate for older teens and adults, and they typically feature characters who are transitioning from teendom to adulthood.
I’m not convinced publishing needs a new category. Heck yeah, I slapped a “New Adult” tag on each of my “Mature YA” books, because I’m not stupid. If everyone is going to say I’m writing “NA,” and that tag helps readers find my books, then by all means, I’ll add it. But what needed to happen has happened: Authors are writing and selling novels with characters in the college age range, without benefit of a distinct category.