I read it. I'm 14. I'm a little more mature than some my age but I read it nonetheless, and I loved it! I'm now thoroughly obsessed with zombies. There were some parts that were kind of gross and unnerving, but it was overall a great book for me and I've recommended it to my friends. It could be a YA book, provided the young adult in question is mature enough and has a sense of humour, because while this book isn't a 'funny' type of book, of course you need to realize zombies aren't real and anyone who actually believes in them and reads this book will go insane and go into a psychosis. This book almost makes zombies seem real. I love it.
in conclusion, yes, this book is suitable for most teens.
Anne Frank is a COMPLETELY different book than this. I am 13 and have read both, and I found "World War Z" to be much more disturbing, but something I could handle and very well written. The difference between the books are that Anne Frank's diary was real, and the war ended, that nazis lost, it was a tragedy but in the end good triumphed over evil. But in this book, I tells of chilling events to come, and lets your mind create the gory details. I think if your kid wants to read it. Let them read the account of one victim, and then decide if they want to read the rest. You shouldn't decide whether or not your kid can handle this based on Anne Frank's diary.
No, it's not a young adult book unless the teen in question can deal with the deaths of 200 million Americans described in sometimes clinical, sometimes gorey fashion. This isn't a "creepy" book. It isn't a happy book at all. It deals pretty realistically with bad governmental decisions, cover-ups, and the horrifically painful collapse of civilization into the worst war in all of history. It's by and far different from any zombie book ever written (and I teach Modern Speculative Fiction)---this book also has little suspense. It's an "after-action" report----there isn't one bit of white-nuckled excitement.
It's still a very beautiful, approachable book. If your teen could handle "Diary of Anne Franke" and enjoy it, then this book might be ok for them. Stop for a moment and think: the realistic portrayal of the deaths of 200 million people due to what is essentially a plague---and that's just in the USA. No suspense. Just death and more death. The book is lyrical, and eventually hopeful, but it is not for moment happy. Beneath age 16, no way.