The New York Times's Catherine Rampell had a dispatch over the weekend making the same point we made here Friday — that growth and the debt/deficit problems are related. She got into the demographic differences between America's postwar growth boom and today, writing, "the structure of America's federal spending is different now than it was in, say, the immediate postwar decades. Back then, growth helped to erase the debt. But remember that in the 1950s, the United States didn't have Medicare. The population was younger, and Americans didn't live as long." She wrote that "whatever Washington does, many economists say the situation will grow only worse, particularly as Americans age and Medicare costs spiral higher." (Emphasis added.)
This link between age of the population and growth rate is an intriguing one, and probably underexplored. There's a Russian economist named Ivan Kitov who has done some work on it. Wikipedia has a list of countries by median age, and the list of those with the youngest populations — Yemen, Chad, Congo, Uganda — suggests that youth alone isn't a guarantee of economic growth. The list of those with the oldest populations — Japan, Greece, Spain, Italy — do include some of the countries that have had slow growth or come under government budget pressure.
If one did think there were a link between age of the population and growth, there would be things that could be done about it, ranging from welcoming younger immigrants to America (green cards for foreign students who graduate from American universities) to Israel-style IVF policies. The Wall Street Journal had a pretty good growth editorial over the weekend but the word "immigration" did not appear in it.
One other point: It's easy to romanticize that postwar growth boom of the 1950s. But the 1950s were an era of slow growth compared to the 1960s, which is when growth really took off. One can attribute that to baby boomers entering the workforce (though the boom predated that) or to women and more minorities entering the workforce (though the boom predated a lot of that, too), or to the Kennedy tax cuts, spending restraint, and military buildup. Or perhaps there is some other explanation.