From the submitter:
We were gonna have him jumped in on his 5th birthday but we had cake and a water balloon fight instead.
Clay won the gold medal in the javelin throw in 2008, and now works as a motivational speaker touring the country. Clearly his Olympic-caliber skills are handy around the house too!
Mahiro here is practicing the Kankudai (or Kanku Dai depending on which hastily-googled page you're looking at), one of the more advanced routines in karate.