Final answer:
The substantial number of retirees in the U.S. began in the post-World War II era due to Social Security and Medicare. The demographic changes led to the phenomenon known as the 'graying of America,' increasing the elderly population significantly.
Step-by-step explanation:
Only since the post-World War II era has there been a substantial number of people who are retired in the United States of America. Significant increases in the number of retirees can be attributed to the introduction and expansion of Social Security and Medicare, as well as the improvements in living standards and healthcare that have led to longer lifespans. By the 1960s and 1970s, a third large decline in the number of working older adults was evident, likely due to the social support provided by these programs.
The graying of America is a term used to describe the increasing proportion of the population that is elderly. When Social Security was initially created, it provided economic protections including retirement benefits for workers at a certain age, facilitating retirement. This, coupled with increased life expectancy and the aging baby boomer generation, has led to a larger retired demographic and a shift in social institutions and public policy decision-making surrounding retirement and health benefits for the elderly.