Kishimoto seems to have either confused the timeline, or has greatly massaged the timeline, if young Oonoki can talk about the Hokage Monument (which was made around the time of Konoha's founding) and then show teenage Oonoki fighting Madara. So, Madara either rebelled years after Hashirama was chosen to be Hokage (which goes against everything we currently know) or Kishimoto messed up the timeline. (It certainly doesn't help that Konoha was the first Village, yet Iwa seems to have age-old traditions already in place...)
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