These charts from the New York Times are just the kind of thing I've been looking for.
Here is the static version of the chart from the article. It would be great to see a moving version of this over a longer period of time.
I'm not sure there is much to worry about on the age groups under 50 years. Some blame the increase in young workers not working while in school on the minimum wage. There might have been some of that after the 2007-2009 hikes, but the minimum wage is nearly back to insignificant levels, so I can't believe it would have had that much of an effect. And, we saw this same trend between the MW hikes of 1996 and 2007. So, I think this is largely a cultural shift.
Between 25 and 50 years, there has been a shift to unemployment, which is cyclical and should be generally temporary. Otherwise, there have been small shifts to disability and caring for family.
I would also attribute much of the drop in rates of retirement to cultural changes, generally from people being more productive and active at older ages. Some attribute this to older workers lacking retirement support, but as with the young, this represents a long term shift in behaviors that has persisted through business cycles. There is a tendency to negativity in some of these interpretations, so that lower labor force participation in 50 year olds is blamed on stagnation and higher labor force participation in 60 year olds is also blamed on stagnation.
The largest problem is the disability issue, which affects the over 50 age groups the most. This is clearly the product of bloat in a program that has devastating moral hazard issues, and it appears to be a significant input into the decline in US labor force participation compared to other nations over the past couple of decades. Other public programs have the problem of creating a high de facto marginal tax rate for the poorest households. But, this policy provides a meager support level and then explicitly directs recipients to self-identify as unproductive. Local news teams expose frauds on disability who are filmed playing in softball leagues, etc. This is trees and forests, people. We're the monsters that put them in that situation. (Of course, you could say the same for banks overleveraged on AAA securities.) I predict that this problem will not be a topic in the political theater associated with upcoming elections.