When was the first ever calendar system developed?

Some cursory googling suggests that the earliest known prehistoric calendar monument is Warren Field in Scotland, or possibly Wurdi Youang in Australia, and that the earliest known written calendar system was Sumerian.

However, I also keep coming across the claim that the Yoruba calendar 'Kojoda' is the earliest/oldest calendar, but I can't find anything that goes into detail around the evidence for this claim.

When was the first ever written calendar system developed? Did lots of calendar systems develop separately across the world or just a few which then spread?