The 3 different stories I heard about the origins of JJ, Kung Fu, etc etc are as follows:
1. There was a monk, a single monk who crossed some sort of threshold and created the ultimate martial art. He then traveled the world spreading this. I remember it being stated that this occurred in the 1500's, but I could be wrong.
2. That it was through immigration of the people from India. In this case I would wager that its based Kalarippayattu,
http://en.wikipedia.org/wiki/Kalarippayattu If you dig even deeper than that, its hinted that early/pre Kalarippayattu was influenced by Alexander the Great's army, which as Greeks would practice Pankration. Which would put the age in the 4th century BC.
3. That each region developed their own martial arts. The idea here is that we all have 2 arms and 2 legs(-amputees), and that even though there might be one great thinker/fighter per generation, every civilization has one. Then through wars and competitions they learned from each other. In this case people have been fighting each other and doing versions of JJ since we learned to communicate.
