Calculated Risk often emphasizes the importance of demographic changes: the decline in participation rate due to the aging of the baby boomers, the decline in immigration.
I thought I'd check the the GDP per capita. This is what I got through a Google search (the image is a bit scrunched here--google it yourself.
What it seems to say is, after the dip of the Great Recession, we're growing the economy on a per person basis quite steadily. Because the level of activity of the overall economy varies with the change in population, particularly net immigration, we see more variance in the economy than at the person level.
Of course, this says nothing about the distribution of economic benefits among the population.