First of all, we have no good data before the middle of the 20th century.
And I think you need to take
trix' argument into consideration. There is a difference now that we haven't had for about a century: the background condition of a rising America has been flipped by conservative policies and America is now in decline for all but the super rich. It was rational behavior for people to become complacent as they got older when they were on an up escalator. But America post-Reagan is an empty elevator shaft (just as it was designed to be by the people who lied to put those policies into place). Why would people relax into conservatism when conservatism has destroyed the American middle class that liberalism built in the first place?
The decline into social conservatism with age will still exist: the bigotries they picked up as children are eroding in the wider culture so by standing in one place they appear to move to the right as their older, even more bigoted parents and mentors die off and are replaced by younger, more tolerant people.
And the Sex Envy/Anger/Futility of the Olds will always be a factor, as they respond to their diminishing powers and attractiveness by trying to force control of women's bodies and choices and promulgate the superstitious Sex Fear that the Olds are always prey to as they near death.
But decline into economic conservatism is not a natural law. It was a rational choice as people moved into the Haves, but in a broken system which is shrinking the number of Haves, you'd expect the Olds to be just as p-ssed off and ready for reform as the young.
