First, I can't predict what will happen in the next 30 days. I keep asking people that should no, and I'm not getting great answers. I think we all continue to assume this is political theater and will get worked out before the fire starts.
Second, let's try anyway. Millennials are the largest group, slightly larger than the Boomers. They are entering their prime earning years- saving, having kids, buying homes, etc- but their salaries on a relative basis are less than Boomers pulled in. I think 20yrs is too short a time to kill off the Boomers as some are just approaching 60. That said, in 20years, Boomers go but the Millennials will be hitting retirement. That change in mix makes predicting 20-30yrs hard. What is a good bet in the prediction is that Millennials are not paying enough into SS and Medicare to compensate for what they will take out, so the problem doesn't go away. We are not going to go backwards in medical advancements, they will not get cheaper, and people will continue to look toward retirement about two weeks after they start working.
Regarding markets, a good example is that we thought as Boomers advanced to and thru retirement they would move away from stocks and into bonds, thus causing equity returns to decline and bond prices to increase (prices up/yields down). We got the latter, but equity returns held up very well. The result of money printing??? Maybe. But we did see net outflows from equities for at least the last 15 years. It's just that equity prices remained strong.
I think part of our collective anxiety stems from out inability to process large numbers. A billion, a trillion, etc. We have no scale. Like trying to think about dinorsaurs living 50m years ago. We just don't comprehend. Citadel CEO Ken Griffith made $22Billion last year. That is $700/sec for every second of the year (31.5m of them). Try spending that. And we are supposed to empathize with him when he moves the firm to Florida for tax reasons?