As much as I want to dismiss this you actually raise a pretty good point. On top of that an argument can be made that Hidan may have even outlived the SO6P. Because if you think about it anyone of that Caliber should be able to use Ninjutsu, and yet he does not? Perhaps he doesnt even know how to mold Chakra. Which could be a hint that he was born in a time when there was no Chakra and/or Ninjutsu.
Then again you could bring up the Samurai who also dont use ninjutsu or any other scenario where he could have grown up not knowing ninjutsu. But still a good argument can be made that he may have preceeded the SO6P.