You would have heard it from me here on FR -- on any threads where the labor participation rate was being discussed.
I was really surprised to learn that in the official measure of labor participation rates, an 80 year-old man who is retired, plays golf every day, and has no interest in working is counted the same way as a 40-something man who would be considered a "discouraged" worked not actively seeking a job.
But when the unemployment rate began to fall during Obama, many conservatives grabbed hold of labor force participation as proof the real rate was still high and getting worse. I often asked what the rate should be. Never got an answer. Just that the rate was proof that the unemployment numbers weren't really looking all that good.
Like you, I too was surprised at who and what made up the stat. Basically if you're over a certain age (16 I believe) until you're no longer fogging a mirror, you're in the stat. And yes, for the last 4,5 years or more boomers have been moving out of the labor market with increased velocity. But prior to Jan of 17 you seldom saw that as a factor in the falling or stagnant labor force participation rate.