Unfortunately this is economic bullshit. They are taking a description of an economy that requires a constantly increasing workforce and increasing productivity and then apply the most obvious, ill-thought out short-term fix, and actually expect it to work despite violating the basic assumptions.
Population growth stopped 15 years ago. Normally those people that weren't born would be entering the workforce in about 5 years. So with quite a bit of variability, the new people coming into the workforce will drop of a cliff. Extending the age of retirement has already (if "temporarily") stopped the outflows out of the workforce that are going to stop.
This means that the total workforce will drop anyway. Even if people don't retire.
Second they assume productivity will keep rising. But productivity (amount of $ per hour of work) has been dropping for 30 years, initially still compensated by rapid workforce increase, but not anymore since 1995 or so.
The government has spent a ridiculous amount of money (~100% of GDP) to increase the money supply to make it seem like this hasn't happened, but of course the change has in fact happened. The question is how long can we keep spending like this. 100% GDP is a worldwide stat and roughly means that for every dollar anyone, anywhere spends, the government lent and spends 0.08 dollar yearly to, firstly, pretend the economy is not shrinking, secondly, keep the local social welfare going (for the US that partially includes the military, which is in some ways a social welfare program). Every year. Since about 2000. And of course, this has been on an exponentially rising trajectory, with 2 huge growing peaks. One right after 2000. One right after 2008.