How old was the author of your favorite fiction book when they wrote your favorite book?

This is just an experiment I wanted to do to see if authors' earlier or later works are more likely to be favorites. Just write the age of the author when they finished writing the book (which usually means publishing it, unless there were some extenuating circumstances where it was finished but not published like censorship or something), naming the book itself is optional. I will pass on this since I don't feel like I have enough reading experience to name a favorite book with lots of options to choose from.