I had that idea when I was 24 years old. I sat down and tried writing it and thought, "This is a really good idea, and this isn't very good writing. I'm not good enough for this yet, and I will put it off until I'm better."
And I'm glad I waited. I think it's a better book than I set out to write 23 years ago, and I feel like the gods smiled on me, and I got very lucky. Normally, in anything I do, I'm fairly miserable. I do it, and I get grumpy because there is a huge, vast gulf, this aching disparity, between the platonic ideal of the project that was living in my head, and the small, sad, wizened, shaking, squeaking thing that I actually produce. And then there is The Graveyard Book, which is, I think, the first time I've felt really satisfied.
Having spent the best part of a decade trying to write a novel that would do some justice to the idea that inspired it, I found those words very comforting. Contrary to one of the central myths of our society, some things take time. The book written to the publisher's deadline is more likely to be a 'small, sad, wizened, shaking, squeaking thing' than the book that is allowed to come to birth naturally.