The downward elbow in the 50 to 60 age range isn’t because employers lower salaries on older workers to match output. They terminate them, which leads to an unfortunate loss of institutional knowledge. It’s too bad there’s not a better way to handle the pay to output discrepancy of the wiser workers.
I do realize that that may very will be part of it, but I think that, given the way that they acquired the data in the population it covers, that downward trend is likely a large part of the natural process of people leaving the workforce as they retire, with a commensurate downturn in income.
I recognize that there are lots of places that do trim older workers from their workforce, and as a result of the shortsighted philosophy, they lose valuable workers who have valuable experience.