Many European and Mediterranean-based peoples inherited the ancient Sumerian-Babylonian sexagesimal system of time keeping, using 24 hours in a day, with hours of 60-minutes each, and 60 seconds per minute.  There are still today 360 degrees in a circle due to the ancient Babylonian year of 360 days.  (That all changed after the catastrophe of 701 B.C.)  Now our year is about 365 1/4 days long.

Many used the Moon's cycles, in 28-29 day Lunar calendars, trying to reconcile this regular (monthly) movement with the annual Solar cycles.

Calendars of ancient peoples help to confirm the Biblical time frame. They point to a 6,000 year span (or shorter), which is consistent with a literal reading of the Bible.

The Chinese calendar, for example, is at about the year 4717 (in 2020). It appears to mark the birthdate of Noah (or some other pivotal event), from some 300 years before the Great Flood. Their civilization does not at all predate that time. But they have laid claim to this particular starting point or starting person's origin.

The Mayan Calendar was reset in 2012.  Of course some had predicted the end of the world then, but its origins plotted backward date back to 5,125 years ago, or to about 400 years earlier than the Chinese reckoning.

Many calendars have been passed down from Ancient India.  The Mahabharat calendar began about 3,200 B.C.  That would put its start between the Mayan and the Chinese calendars, i.e. from some event in the pre-Flood era.

The origin of the ancient Egyptian Calendar is still debated.  Some contend that it began about 4,500 years ago, others that it began a little before 6,000 years ago (4236 B.C.).  (Both are consistent with Biblical chronology.)

No civilization has a calendar going back for 15,000 or 20,000 years.  But evolution contends that humans have been humans (mentally and physically) for well over 100,000.  Now wait, if that is true doesn't it seem like someone somewhere would have devised an accurate calendar long before the Bible's contended date of about 6,000 years ago?  Once again, real science and real history lines up just fine with the Bible's contentions.  But evolutionists have to ignore the evidence in order to pretend that their theory is plausible.  They would claim that humans wandered around (figuring out fire and the wheel) for several tens of thousands of years - and then "poof!" suddenly on every continent, within hundreds of years of each other - they all decided to start inventing calendars?

The stories of an original ancient paradise (like the Garden of Eden) persist around the world.  Created by God(s), long life spans, a perfect environment, and early civilized men who later fell to violence and evil are all part of these stories.  See Frazier's book.  And then God(s) caused the worldwide Flood, as has been recorded around the globe in various traditions; there are hundreds of flood legends.

Not only cultures, but organizations want to establish their historical stability.  In Italy some can trace their roots back to the remnants of ancient Rome.  In Japan many families can trace their ancestry back to the Shogun times. Or in America for example, "Daughters of the American Revolution" (as one organization) can point to a long heritage. Wanting to establish a strong past has been important for many peoples.

Establishing credibility or seniority - this happens today. Certainly past peoples did so as well. The Egyptians appear to have tried to get their "origins" to be older than others. Did they exaggerate? The Sumerians somehow dated the life spans of early rulers into the "thousands" of years. It is an interesting exaggeration of the true pre-Flood life expectancies of the pre-Flood patriarchs. They actually lived up to around 900-950 years, per the records in the Book of Genesis.