I listened to this on a long car ride with three boys between 11 and 13. My thirteen year-old actually stopped playing a video game to listen (a first) and my eleven year-old didn't complain about the long trip even once (another first).
The story is fascinating, and the intense and gruesome parts from the adult version are toned down perfectly for older kids and still good for adults. I think I would have let my kids listen to this as young as 8 or 9 maybe.
One warning , if you are heading to the beach - there's a fair bit about shark attacks.