Tens of thousands of years old at least, lots of mummies and corpses have burial adornments and items that indicate they were the leader of the pack in the same way rulers later were and are buried with ceremonial offerings and adornments and written descriptions of them being a ruler.

As far back as we have any evidence for.

Aboriginal Australians might be interesting for you to look at as they had a much looser authority structure as nomads and have a societal history of 50,000 plus years old now(keeps getting updated as more sites are found).