Interesting question in post #1. The earth rotates ~ 0.46 km/s and has a 24 hour day. Exoplanets can spin perhaps slower and faster. The primoridal earth after the Moon forming giant impact likely rotated with a 3-5 hour day or ~ 3 km/s.
What evidence shows biological life would age faster or slower on a planet spinning 0.46 km/s vs. 3 km/s?
FYI. There are reports of Earth's rotation faster in geologic time. Here is an 18 hour day in the Precambrian, https://www.sciencedaily.com/releases/2018/06/180604151200.htm, thus Earth could be spinning at the equator ~0.62 km/s. Here is another report during the *age of the dinosaurs*, https://www.sciencedaily.com/releases/2020/03/200309135410.htm, ""Summary: Earth turned faster at the end of the time of the dinosaurs than it does today, rotating 372 times a year, compared to the current 365, according to a new study of fossil mollusk shells from the late Cretaceous. The new measurement informs models of how the Moon formed and how close to Earth it has been over the 4.5-billion-year history of the Earth-Moon gravitational dance." "Earth turned faster at the end of the time of the dinosaurs than it does today, rotating 372 times a year, compared to the current 365, according to a new study of fossil mollusk shells from the late Cretaceous. This means a day lasted only 23 and a half hours, according to the new study in AGU's journal Paleoceanography and Paleoclimatology. "
Thus Earth rotated ~ 0.47 km/s.
Using this data from the fossil record, does this show biological life ages were different than today?
Interestingly, a faster spinning planet has two changes that are included for the final time difference when comparing the rates of time for the same planet spinning slower.
The faster speed slows time due to SR (special relativity). But the faster speed reduces the gravitational effect (centripetal force) found in GR, which increases time. Satellites require the equations of both SR and GR when calculating GPS distances for this reason.
However, the actual time difference would be quite trivial since a planet would have to spin incredibly fast to amount to any real difference, no doubt.
The thing about relativity is that time ticks the same for any given inertial frame. The discrepancy arises only when another person is in a different inertial frame (say on Earth) and they want to tell you (on a fast spaceship) that you have a clock problem. Your response to them would be that they have the clock problem.
The experience of either party for the life expectancy would be the same unless one inertial frame is changed to match another -- the twin returns home younger, for instance. The two would argue that they aged at the rate they expected (24 hours per day per their clock) but they would not argue that the traveler must have had a slower 24 hours per day than his twin.
So, the aging process would all appear to be the same regardless of a planet's slowing. So things like the decay rate of isotopes would happen at the same rate. But, if we could review what happened from a different inertial frame (e.g. Moon), then the decay rates would be off over eons. The problem in this real case would be that the inertial frames are essentially the same when it comes to any real relativistic time differences; the tiny differences would be lost in the ability to achieve the incredible levels of accuracy needed to find a decay rate difference, IMO.