Suggested by Shaker DesertRose: "Do you remember the first adult (as in 'not written for kids,' not as in 'sexy') book you read? If so, what was it? How old were you? Have you re-read it in more recent years?"
I'm sure this wasn't actually the first "grown-up" book that I read, but the first one I can remember is Pet Sematary by Stephen King. My mom was a huge Stephen King fan at the time, and I asked her if I could read it, and she said yes, as long as I promised to come talk to her if anything scared or confused me. It was published in 1983, and I think I read it fairly soon after she read it, and she would have read it as soon as she could get her hands on it, so I was probably around 9 or 10.
At the time, watching horror flicks at slumber parties was THE COOLEST THING, so it wasn't even a little weird I was reading horror novels by the time I was a tween. Ah the '80s!