We have 95 million people between 16-65 out of the workforce. Automation is increasing productivity and eliminating jobs, especially low skilled ones.
Immigrants grow old as well. We could increase legal immigration to 3 million a year from the current 1.1 million and it would have a negligible effect on our aging population.
It’s interesting you mention the 95 million people out of work. Part of what you are describing can be illustrated by the Pareto Principle. Named after an Italian economist named Pareto. Take a look at that and then it makes more sense. The 80/20 rule.