Check out the dynamic graph below that represents the US age distribution from 1933 to 2100. It starts as a narrow pyramid with a relatively even age distribution narrowing as it gets to older ages. Then it takes on an arrowhead shape as the dearth of births during the Depression begins to work its way up through the ages. This quickly changes to more of a spade (playing card, not shovel) as the Depression birth dearth is followed by the 50s Baby Boom. That bulge keeps working its way up the age progression until about now, when the boomerang generation begins to catch up with its parents.
The age bulge then continues around age 30 and as today's 30 somethings get older, the so-called pyramid gets increasingly top heavy. As we move towards future projections, the choppy graph that represents actual people smooths out. The chart creator, Stephen Holzman, then adds colors and shows a broadening range of possible population outcomes. As the so-called pyramid develops, it becomes widest at about age 70, then becomes almost flat at the top as few 70-year-olds make it to age 100.
What's clear is that the average age of Americans is going to keep increasing. What started as a very narrow, sharply-pointed spearhead 80 years ago, with fewer Americans at every extra year of age, will become a blunt wedge 80 years in the future. At the same time, after the Boomers and Boomerangers pass from the scene, there will be a more uniform age distribution which should by itself have an effect on how the generations develop and relate. Of course, projections of uniform birthrates may be upset by the reality of booms and busts, or at least boomlets and bustlets.
It's also interesting to note that the huge surge in the US population during the past 80 years will not be repeated over the next 80, at least as projected. The population that was 116 million in 1925, grew to 152 million by 1950, 216 million by 1975, 282 million in 2000 and 321 million today. According to one set of projections, it is projected to grow to about 340 million in 2025, 360 million in 2050, 365 million in 2075 and 368 million in 2100. This slowing growth rate may be better seen in following chart.
These projections that the US population will essentially stop growing after 2050 and that we now have almost 90 percent of the number of residents as we will in 2100 depends on a continuing decline in birthrates and no increase in immigration. Any change in either could significantly change these projections.
The Census Bureau's projections predict significantly faster, though still slowing, growth, but only go out as far as 2060. The Census Bureau predicts that births will gradually increase from about 4 million a year today to 4.5 million in 2060, deaths from 2.6 million today to 4.1 million a year in 2060, and immigration from 1.25 million people a year today to 1.5 million in 2060.
Of course, the last figure on this chart shows only 10 years of growth. Ten percent growth over 25 years would bring the US population to approximately 440 million in 2075 and undoubtedly a somewhat broader shaped population distribution than that outlined in the GIF above. Of course, few of us will live long enough to see which projection proves correct, but our children and grandchildren will.