Why are you asking this? I mean why aren't you asking about that region, or Shan State, or the first Wa inhabitants? Why are you asking about a couple tiny spots of Shan state in particular?

It would help in giving you the answer you might actually be after. Otherwise there's something fishy about it.

The answer is "sometime around the Pleistocene" based on the archaeological record. There's reason to believe that it goes back further a ways. But these weren't Wa people, which is also why I'm curious about your reasons for asking this particular question.