An interesting statistic is the relative percentage of the US population of working age (i.e., ages 25–64, to be conservative) and those 65 and over, based on US Census Bureau data and projections. The percentage of the population aged 65 and over is currently about 19%, but is expected to increase to 26% by 2070. This has implications for how the OASDI (Old-Age, Survivors, and Disability Insurance) program is funded. Of course future immigration could change these projections.
Link: https://www.census.gov/data/tables/2023/demo/popproj/2023-summary-tables.html