The problem the American working class has isn't something that can be easily fixed in the short run for Americans, unfortunately.
Americans from the 1940s to the 1960s benefited from half of Europe being rubble and the other half being Communist controlled rubble, letting them basically dominate manufacturing, trade, etc. That was obviously unsustainable, first with post war reconstruction kicking into gear for Germany, Japan, etc and second with the industrialization of places like China and Kenya. The post-war economy of the US isn't coming back unless WW3 happens and it somehow doesn't involve the US.
Mind, regular people in the countries where industry is being exported are benefiting pretty substantially, and the (theoretical) long run result of all this is that people in China will rise to the level of wealth of Americans, whereupon the jobs will be exported to poorer countries until global wealth is more equalized (by country anyway, not by class).
I don't understand the economical fear of having less young people versus old people.
Last two times that happened, most involved countries saw economic growth, not recession. Except Germany after ww1, because peace treaty fucked them over too hard.
I mean, after ww1, most countries were left with only elderly and small children. All people of healthy working age died in the trenches. Yet their economies didn't collapse, they boomed. The period after ww2 is similar, albeit less severe, since it saw less military dead than ww1. It only wiped out half a generation instead of a whole one.
So don't fear the grey, just legalize child labour and we'll be fine.
Most countries after WW1 didn't have expansive welfare states, universal healthcare systems, old age pensions, etc that needed large growing economies to maintain. The ones that did exist tended to pegged to revenue generation rather than "benefiting the masses" (eg. in Germany, the old age pension was set high enough that most people died before receiving what they put in so it functioned as a hidden tax), so they weren't a huge burden on the government to provide.