Should young adult books have labelling for mature themes?

I am a parent who is interested in what my children are reading, and would like, one day, to open a book shop. I have a fourteen year old boy who is a very capable reader. Thus, I have been reading some books in the young adult genre. I recently picked up "The Nest" by Paul Jennings, the author of children's beginning readers such as the Rascal the Dragon series and books such as Wicked. I read the blurb - a book about difficult relationship between a boy and his father, an unsuitable girl who's pursuing him, and mystery surrounding his mother leaving them when he was a baby. The sort of topics I would expect from a book shelved in the Teenage section of our local library. My son read the book, and then said "you've got to read this, mum". "Why?" "It's different and interesting" (in a weird way was the implication I got). This is from a boy who has read "The Da Vinci Code" and the whole series novels written by Matthew Reilly.

Well, I have just finished "the Nest". I agree with most of the reviews I have subsequently read that it is well written, dealing with topics that teenagers are being exposed to, and clever in it's construction. The problem I have with this book is that I chose it for my teenager to read based on the blurb on the back cover and the reputation of the author. On reading it, I was a little shocked with some of the content - nudity, drug use, murderous thoughts by the 16 year old main character.

My question is - is this book suitable for a child under 15 (no matter how mature they appear these days, they are still children) to read? Would I be happy for my 12 year old (who is also a very capable reader and borrows books from the teenage section) to read this book? To be honest with you, no, I wouldn't. However there was nothing on the cover or front pages of the book to alert me to the fact this book wasn't really suitable for under fifteens.

This is not about the ability of the reader, it's about the maturity of the reader to understand the concepts in the book. This issue is not restricted to just the young adult section. I often see children who are quite capable readers, reading books which has content which they don't understand as they have no life experience of the emotions or events which the characters are dealing with. Over the years I have had many discussions with my children's teachers on this point.

What is my son's opinion? When I quizzed him on whether the content of "The Nest" was appropriate for children younger than him - his response was , "they all have it".

I think I'm getting old.