Board Thread:General Discussion/@comment-5501448-20160509010655/@comment-26812877-20160512030224

Look up the Ben 10,000 character page. It states in the trivia that Ben was originally supposed to become Ben 10,000 at the age of 15. There are even links on that page that proves it. I believe that was also mentioned when CN did that trivia pop up marathon of the Original Series almost 8-10 years ago.