The earliest event where we have a date which we can convert into the modern Calendar is the Battle of Megiddo which according to the Egyptians happened on the 21st day of the first month of the third season, of Year 23 of the reign of Thutmose III. Now converting that into the modern calendar we get the date of April 16th 1457 BCE. There are events that occurred earlier but the exact date is unknown.

Can I ask, are there not mayan/incan events or festivals which coincide with easily identifiable and datable astronomical events? eg. eclipses?

Or other societies, such as the Egyptians? It seems to me that this would be an easy way to accurately date an event.