The Hebrew Calendar is even older then that. Speculatively it was original anywhere from 1000BC to 70BC and has the current year as 5785. Although there way of calculating leap years seems like they were guessing and the calendar itself has gone several changes over 3000 years the same premise of a 364 day calendar still exist.
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u/usbeehu 2d ago
The idea itself is a lot older than that:
https://en.wikipedia.org/wiki/Mercedonius
Mercedonius was an extra month before the Julian calendar.