Honestly, it's probably above a 13-year old. I'd say a 16-year old with good language skills. We originally conceived this as a "text" book but realized that it would never get by the various faculty committees, and moreover, we learned that a "text" book cannot even GET IN A BOOKSTORE! My book, "The Entrepreurial Adventure" (2000) cannot get into Barnes and Noble or Borders. So we took the "trade" route with this one, and I'm glad we did.
Just tell your 13-year-old to hang on for a couple of years :)