The graying of America's workforce will come as no surprise to regular readers. Just earlier this month, we wrote that in a little noticed aspect of the "stellar" June jobs report, the vast majority - or 90% of all new jobs - went to workers 55 and older.

Hardly an outlier, this was the latest confirmation of a very troubling trend: all jobs created since the recession started in December 2007 have gone to workers 55 and older.

In fact, in the latest month, there was a record 34.5 million workers in this age group: the only one that has seen persistent growth this century (and with the concurrent surge in waiters and bartender jobs in recent years, we even have a sense of what they are doing).

We won't go into the reasons for this dramatic divergence (we have covered it extensively in the past); instead we bring up these observations because according to a new NBER paper, this stunning trend is what is being used to scapegoat the accelerating collapse in US productivity. As Bloomberg reports, "population aging is expected to drag on U.S. growth, and the hit could be substantial."

According to the National Bureau of Economic Research, the retirement of baby-boomers in the decade between 2010 and 2020 will lower GDP growth per capita by 1.2% a year from what would have been the case if the nation's demographics had held steady, while slamming productivity.

The thinking behind the study is simple: population aging is already long underway and by looking at variations in state population aging, authors Nicole Maestas at Harvard Medical School, and Kathleen Mullen and David Powell at policy research group RAND Corporation, are able to estimate how a graying workforce affects output, participation rates and productivity.

Now America's deteriorating productivity trend is nothing new; however for the first time it has been blamed on the demographic shift of the US workforce and specifically the vast preponderance of baby boomers stuck in the labor force, instead of - say - half the population of the US and Canada using Facebook on a daily basis. As Bloomberg adds, what's surprising is the composition of the slowdown: one-third is driven by slowing workforce expansion and the rest by a drop in productivity gains. The productivity slump isn't reserved to older workers: it takes place across age groups, the researchers find.

The authors suggest a few theories about why that's the case. It could simply be that younger and older workers complement one another. Or the most productive older workers might be leaving the workforce, while less-productive old timers stay on the job.

This is another way of saying that employers keep hiring old, experienced workers at the expense of younger Millennials who are unable to find jobs due to bottlenecking as a result of the same older workers who refuse to retire for no other reason but simply because their savings no longer generate a cash flow.

"How much of it is that relatively productive workers are the ones who are choosing to retire? It's very hard to say," Maestas told Bloomberg.

Regardless of what's behind it, the discovery that the aging workforce could be weighing on productivity comes in contrast to other guesses, is important. The Fed has long been pondering over the issue of sliding US productivity. As Bloomberg adds "it's not clear why productivity growth has dropped off, and the change has real-world implications: it's one factor that caused Fed officials to lower their projections for where interest rates will settle in the longer-run, based on meeting minutes from their June meeting."

What's worse about the new findings is the suggestion that already slumping productivity is set to get even worse. If growth over the next 20 years otherwise held near its average for the 1960-2010 period — about 1.9 percent — adjusting for the demographic shift would lower per-capita GDP gains to 0.7 percent this decade and 1.3 percent next, based on the estimates.

It also means that the natural rate of growth is likely at or below zero, which also confirms that any attempts to hike rates will be doomed to failure as the US economy simply can not sustain a rising cost of money, thus forcing the Fed to ease after every single rate hike.

But while we agree that the relentless aging of the US workforce will have dire implications for the future of the US productivity, as well as economic growth, it is clear that the study never got to the fundamental culprit, which is the Fed itself.

Because the glaringly obvious tangent is that old workers are stuck in what now seem to be "lifetime" jobs, with no hope of retirement, for one overarching reason: the interest income generated by savings is zero (and negative in real terms). This means that as an entire generation of workers has found out the hard way it will never have the planned cash flow from savings parked in the bank; it is therefore doomed to work until death. By implication, it also means that the entire younger generation, in this case the biggest one in US history, the Millennials, will be stuck unable to enter the workforce and to build critical labor skills, as a result of lack of hiring as employers retain their old, experienced, and thus much more cost-effective workers for as long as they possibly can.

Our advice to the Harvard authors of the study: in the next part of the study, the one looking at why the US finds itself in this situation, please look at the Fed's monetary policy. Because with over $10 trillion in savings generating no income, and thus crushing the velocity of money, the real reason why the US is facing a productivity crisis of epic proportions is because the central planners in the Marriner Eccles building have destroyed an entire generation's hopes of being able to retire.

As for those elderly Americans stuck in menial jobs until their dying day, our condolences.