[hypersoar]

Using overall life expectancy here is misleading, as it includes the risk of childhood mortality. You have to look at life expectancy at a given age. According to the SSA's life tables[0], life expectancy for men at 65 in 1930 and 1940 was about 12 years. In 2020, it was about 17. A significant increase, but not nearly as extreme as you're saying.

[0] https://www.ssa.gov/oact/NOTES/pdf_studies/study120.pdf

[nofriend]

In 1930, if a person starts paying into the pension at 30, at that point they have a life expectancy of 37 years, ie they will benefit from the pension for 2 years. Life expectancy at age 30 goes up to 48 in 2020, which gives them 13 years after retirement, 6.5 times higher. Assuming linearity, the average life expectancy after retirement during the time you are paying into your pension between 30 and 65 would be 7 years in 1930, and 17 in 2020.