I've been doing research in my spare time lately about how demographics impacts our economic growth, or the lack thereof. The research by Henry Dent and others suggest that the US benefited from a prosperous post WW2 generation buffeted by programs like VA Home Loans (making buying homes much easier) and VA college programs which enabled many veterans to attend college after the War. In turn these measurers and others opened the way for an expansive consumer class. A college degree in the 1950s was very much an instantaneous way into the path of social mobility.
The Greatest Generation produced the Baby Boomer generations that also gained favor from a higher education level obtainment, a robust economy started by the Greatest Generation and of course technological advances.
Consequently, between soaring demand and technology making the way for new products the US economy grew at incredible rates, often topping 5%. Once Europe and Japan recovered from the destruction of WW2 they also experienced similar trends.
By the 1980s the Greatest Generation was moving off the stage, retiring and often downsizing and spending less. For awhile the Baby Boomers now approaching their 40s and beyond took up the slack. But 20 years later they began to downsize their lives.
Unfortunately, family sizes from Generation X on got smaller. After the creation of the Internet technological advances have slowed considerably. This has cumulated into lower demand from consumers and a smaller population as specifically among upper middle and middle classes Baby Boomers had fewer children. Both parents wanted careers and birth control made family planning much easier.
Since 2009, we've had one brief quarter of more than 3% growth. Moreover, with more and more Baby Boomers downsizing the expectation is that 0% to 1% growth will be the new normal. Add to this the way in which millennials are buying large ticket items such as homes and automobiles in lower numbers than previous generations.
The end effect is a long term stagnating economy for the next ten years until supply once again meets demand. This will mean companies tied to the consumer industry such as retail will see a major constriction.
I think there is definitely something to this theory and explains to a certain extent that after nearly a decade since the "great crash" the economy in the US, Europe and Japan can't get the desired lift and momentum. In fact, Japan which has even more adverse demographics than all of developed countries has been in recession for going on 30 years.
One final note of course is that all of the population growth is going on in less developed worlds. The restricting factor here is that these people are poor, in some cases desperately poor and their growth in population can't come close to making up for the declines in more advanced countries. Also in the US, pockets of population growth have come from typically the lower end of the income scale, unable to maintain any real purchasing power. The loss of the upper middle and middle class even depresses their economics even further as the working poor often serve the needs of the upper middle and middle classes. Think jobs such as a retail clerk or waiter in a restaurant.
One way to offset what will be temporary factors of meager growth until equilibrium is achieved would be to upgrade and replace our decades old infrastructure. This would help bridge the gap that is being felt in the private sector. However, I've argued this before and don't want to repeat myself.