Take a wild guess as to when the Boomers started writing books.https://twitter.com/boes_/status/866694305691439106 …
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
I'm guessing not when the eldest Boomers were 5-10 years old. Which is when that spike begins.