Demographics impact this data, no? People in college, increased ability to retire, and an increase in the number of retire people (due to an aging population)

Demographics impact this data, no? People in college, increased ability to retire, and an increase in the number of retire people (due to an aging population) all have an effect. What does the data look like from 1900-1948? I imagine WWII had an impact too. I would also consider whether the growth the welfare state is responsible for the drop--rather than just makes up for it.