“Aging” is a bit misleading here - it’s about the society’s age, not the people in it.
I wonder if there is some selection bias. Many potential “civilisations” might not appear in the historical record, if they die too young. That could explain the lower risk of death for the first 200 years.
But Figure 4F kinda suggests it's really unlikely for one to survive past ~300yrs or so? So, yes, not fixed but there is a survival curve (assuming their models are generalizable, which they very well might not be).
From the paper: "In conclusion, the distribution of longevities reveals that the risk of termination rises over the first two centuries, and then remains roughly constant. That is, newly established states appear to have some benefit of youth in terms of survival chances, but this effect fades away over the first ~200 y. Such a saturating pattern (cf. Fig. 2B) is very different from the exponential rise of risk with age observed in humans (cf. Fig. 2C). This difference corresponds to the fact that humans have a more-or-less well-defined maximum age, whereas some states may persist extremely long compared to the average lifespan."
It's worth looking at how this behaves for companies.
The oldest private companies in the world are mostly makers of religious supplies of some kind. Kongō Gumi made it to over 1,400 years building Buddhist temples in Japan, but went bust in 2006. Then there are a few hotels, restaurants, and wineries which have really good locations and have gone on for centuries. They're all tiny companies. Stora Enso, in Finland, founded in 1288, seems to be the oldest non-tiny business still active on a large scale. Italy has some very old banks which are still in operation at a reasonable scale. Breweries seem to hang on for centuries.
The oldest manufacturing company that's a significant company today is Beretta, the gun manufacturer. Founded in 1526, and still making good guns in quantity. Sumitomo, founded in 1615, seems to be the oldest Fortune 500 company.
Very likely tied to some yet to be identified standard decay rate linked to the entrenchment of nepotism and consolidation of power around a handful of non-producing families who are detached from the needs of the people whose culture they, er, cultivate to support their own otherwise impossible existence.
De Toqueville goes into this a little bit in Democracy in America, IIRC his theory seemed to be that traditions of inheritance and entail impart the largest bias on lengthening or shortening the time this entrenchment takes to become pathological.
This seems important and was fascinating to read but it seemed difficult to quantify the lifetime of a state? When does one end and another begin? Are changes in lifespan over time due to actual lifespan changes, or changes in the meaning of a state?
I wonder if there is some selection bias. Many potential “civilisations” might not appear in the historical record, if they die too young. That could explain the lower risk of death for the first 200 years.