The book details the lives of very old, as well as very young, people. How did someone as young as you acquire the insight to write about the experience of being old in such a moving way?

That's what writers strive to do. Though I can't describe the process of writing and how I do it (I don't really understand where my ideas come from), I do keep a few general rules in mind, no matter what type of character I'm writing.

First, I tend to assume that most people -- male or female, young or old -- have largely the same types of thoughts. However, the difference lies in their perspectives. So I try to put myself in their shoes and see the world the way they do. Then, I read constantly and see how other authors have written from varying perspectives and I try to figure out whether they accomplished what they set out to do or if they failed. Either way, I ask myself, "Why?" Finally, I work hard at it -- I edit constantly until it "feels right" to me. Only then am I satisfied.