They include the civilian noninstitutional population, which includes retirees who are not institutionalized in a nursing home: https://www.bls.gov/cps/definitions.htm#population

Then why does my link specifically have a "25-54 Yrs" qualification, and has a totally different shape compared to the first link? The difference between the two is stark, 21.8 percentage points. Do you really think there's that many people willing to work between 18-25 and 54+?