The two plots together suggest that the Plains are losing population in all age groups are are not getting older.
The surprise for me is FL. Not only is the youth population rising, but the share of the youth population is rising, too. Orlando, Tampa Bay, the Panhandle (except Pensacola), and Metro Miami all saw an increase in the youth share.
By 1970 it dropped to 12.6% as increasing longevity of those older, and baby boomers reduced the share of persons born in the latter part of the Depression and WWII. The minimum was 11.9% in 1965.
By 1980 it had increased to 16.5% as Baby Boomers entered that age group, hitting a peak of 17.5% in 1985.
By 1990 it had dropped slightly to 17.2% as the last stages of the Baby Boom were in the age range.
By 2000 it dropped to 14.2% and by 2010 to 13.5%.
Comparing 2010 (13.5%) to 1970 (12.6%), there was a 7% increase in relative share, which placed a green bias on the map.
If the Washington Post repeats their study in 2024, comparing 1980 to 2020, there will be around a 19% negative bias, and the country will be shown in vast expanses of pink.
So WaPo picked a cohort primarily from the Silent Generation for 1970. That also explains the intense green on the map in much of the plains, since the the youth of that generation were known to leave the farms for college and stay in the cities afterwards. The comparison is to a Gen X cohort, so at least they are comparing two groups near the minimum of the population distribution.
