I still haven't read this book yet but want to, simply cause I adore the movie.

Part of why they sound so much older could be due to the struggles they've faced. I know people who face these kinds of challenges at a young age tend to grow up faster than normal, so that could be a factor. Just a thought, but I can't say for sure since I've only seen the movie so far.

The movie is excellent, btw, so I highly recommend it. The actress who plays Hazel is brilliant and if you cry at anything you will cry at this movie.