It's probably suitable for 12 year olds and onwards. Despite the story dealing with `body-snatchers' it is not actually graphic or even really scary and there's no vulgarities except a few kisses here.
My 12 year old read this after reading the Twilight series and loved it! I have to say, I think there is less "adult themes" in this book than in the Twilight series. I found it a bit sklow at the beginning, but once I got into it I couldn't put it down and my girl was the same .