But that was an era when there was still no vaccination against childhood diseases, which brought down the averages. If you survived long enough to enter the work force, and were healthy enough to work, your life expectancy was considerably better.
http://www.ssa.gov/history/lifeexpect.htmlLife expectancy at birth in 1930 was indeed only 58 for men and 62 for women, and the retirement age was 65. But life expectancy at birth in the early decades of the 20th century was low due mainly to high infant mortality, and someone who died as a child would never have worked and paid into Social Security. A more appropriate measure is probably life expectancy after attainment of adulthood.
As Table 1 shows, the majority of Americans who made it to adulthood could expect to live to 65, and those who did live to 65 could look forward to collecting benefits for many years into the future. So we can observe that for men, for example, almost 54% of the them could expect to live to age 65 if they survived to age 21, and men who attained age 65 could expect to collect Social Security benefits for almost 13 years (and the numbers are even higher for women).
Also, it should be noted that there were already 7.8 million Americans age 65 or older in 1935 (cf. Table 2), so there was a large and growing population of people who could receive Social Security. Indeed, the actuarial estimates used by the Committee on Economic Security (CES) in designing the Social Security program projected that there would be 8.3 million Americans age 65 or older by 1940 (when monthly benefits started). So Social Security was not designed in such a way that few people would collect the benefits.
As Table 1 indicates, the average life expectancy at age 65 (i.e., the number of years a person could be expected to receive unreduced Social Security retirement benefits) has increased a modest 5 years (on average) since 1940. So, for example, men attaining 65 in 1990 can expect to live for 15.3 years compared to 12.7 years for men attaining 65 back in 1940.