There are, however, other factors, too. The gov't has expanded the safety net to the point where you really don't have to work if you don't want to. Also, parents seem more amenable to the idea of a son living at home, even into their 30's.
This particular item in the narrative is poorly presented and misleading. In fact, it’s probably not even relevant to the author’s underlying point. The reason for this is that the “aged 16 and over” statistic has no upper limit, and the size of the total potential work force in the U.S. includes everyone ages 16 and over who is not in school, in prison, or in a nursing home.
U.S. labor participation rates have declined over the last 80 years mainly because more and more Americans today are RETIRED, not because of any of the factors the author discusses here.