I'd love to be able to please everyone. Honestly, I would. But since that isn't possible, I have to pick a road and drive on it. The stories I write are about people in the 17-22 age range (in keeping with the fact that young people generally like characters who are a bit older than themselves), and they're going to realistically portray those ages as much as possible.
My definition of Mature Young Adult is 17+ (or younger, with parental permission - and if you aren't checking what your kid is reading, you've effectively given your permission).
A review I read recently posed the judgment that "YA Mature" should mean later college at the youngest. UM.
NO ONE in charge of entertainment ratings (these panels are made up of parents) agrees with that statement. First, let's take movie ratings as an example. In the US, at age 17 (generally high school junior), a person may purchase a ticket to see an R-rated or an NC-17-rated movie (or the movie itself) without parental consent. We're not talking words here, folks. We're talking film: harsh language, drug and alcohol use, physical violence, explicit sexual scenes. (Note: He or she may purchase pornography at 18.)
To reiterate: Your 17-year-old high school junior can run down to the cineplex and see any damned movie she pleases.
Game ratings follow movie ratings fairly closely, though the lettering is different. Once again, a 17-year-old high school junior can pop by the local video game store and buy any M-rated game (meaning intense violence, blood and gore, sexual content, strong language) with no parental consent. Adult-only games may be purchased by 18-year-olds, otherwise known as high school seniors. These may include scenes of intense, prolonged violence and graphic sexual content.
Young Adult (YA) literature has a problem. It lumps 14-year-olds in with 17-year olds. Anyone who works with or has kids in that age range knows there's a big difference in maturity between 14 and 17. (If a child is a very mature 14-year-old, she is most likely going to be more mature at 17 than her peers, as well. This is where parental guidance - the notion that you know your own child best - comes in.)
I began choosing YA books for my kids when they were 12/13 and had become bored with MG (middle grade) books. Trust me when I say that it didn't take me long to realize that the ratings for YA weren't good enough. I was going to have to read or skim through everything they wanted to buy until I felt they were old enough to choose for themselves (for my kids: 14).
As an author, I can't invent a book category. Amazon and B&N give publishers and indie authors category choices at publication. My current category (YA) contains no separation between 14-16 year olds and 17-ups. The best I can do is include, in the book description, my own warning/disclaimer, and that's what I've done since I first published Between the Lines.
I'm not required to do this. And by the way, this is not something traditional publishers have been doing. This is something I took it upon myself to do because I was the parent sitting in the bookstore floor, reading the YA books to make sure they were appropriate for my 7th grader. I have zero problem with someone deciding my books are too edgy for their kid. I have LOTS of problems with someone deciding my book is too edgy for someone else's kid.
And please, before you assume that indie authors are running hell-bent-for-leather into sexual situations that no traditional publisher would ever condone, please go read Looking for Alaska (Printz Honor Book), Perfect Chemistry (NY Times Bestseller), Going Too Far, The DUFF, The Sky is Everywhere, the Wicked Lovely series, The Wolves of Mercy Falls series... all of which are amazing, wonderful, traditionally-published, "Young Adult" labeled books with edgy content.
The authors whose works are listed above are well-respected by the publishing world and the general public, as well they should be. You won't find anything in any book of mine that I can't find in a Big-Six published young adult novel (which will include no parental warning by that publishing house).
If the publishing world - which includes Amazon's KDP and Barnes & Noble's Pubit - comes up with a book category reflecting the independence and maturity 17-ups are afforded in every other entertainment venue, I'll be happy to move my books into that category. Until then, I'm motoring down my chosen road, marking it as best I can.