I am a bit of a nerd. Not in the “I know who Kylo Ren is” sense of people claiming to be nerds for being familiar with subsets of pop culture. But in the “I have a favorite set of census data” sense, which I suspect is less common.

I mention it because my favorite set of census data, the count of America’s population by single year of age, was updated this week. And what it shows us is that we’re at the start of a long-term trend in which America gets older and older.

It’s obviously the case that the United States is getting older, of course. Time passes inexorably and all our yesterdays have lighted fools the way to dusty death, etc. etc. But as time passes and as America itself ages, our population is becoming more densely old and less densely young.

By comparing the population by year of age (that is, the number of 25-year-olds and the number of 42-year-olds, etc.) in 2010 and 2020, you can see how that pattern unfolds. Here, in fact, is that comparison, with four interesting components of that shift highlighted.

Let’s start with Box A. (These boxes mostly highlight the data for women, but the same effects are seen for men as well.) You’ll notice that at this point the thin columns, representing 2010, extend well above the thicker columns. That means that there were more young people (ages 0 to 5 or so) in 2010 than there are now. In other words, the United States was doing a better job of repopulating itself, having more kids a decade ago than last year. Last year was anomalous, of course, given the pandemic, but the number of 1-year-olds last year was also lower than the number of 1-year-olds in 2010.

In Box B you can see how America is aging. That bump at the left side of the box representing a small boom in births has gotten older. But you’ll also notice that, as it got older, it also got bigger. The columns in 2020 are higher than they were in 2010. Since you can’t retroactively have more people born in the United States 30 years prior, that’s a reflection of immigration: more 30-year-olds moving into the country.

Box C shows the erosion of the size of a group as it ages, which is to say attrition due to death. This box again shows a mini-bump in the population getting older, but it also shows that group getting slightly smaller.

And in Box D we see the most important group for which that attrition is happening: the baby boomers. That big jump in the middle of the box is the big jump in people born in the years right after World War II.

But notice another shift from 2010 to 2020. You can see that the columns at the left of Box B representing 2010 are lower than the 2010 columns at the left side of Box C, meaning that there were more people at the older age 10 years ago. In 2020, the columns in Box B are higher; the most common age shifted downward over that period.

Between 2011 and 2012, the peak of the baby boom had eroded enough that the oldest year of age (51) was surpassed by the peak in the earlier boom (21). That’s the baby boom showing its first signs of fading.

But, again, that doesn’t mean that America is getting younger. The density of people aged 65 and up increased by nearly four percentage points from 2010 to 2020 while the density of people under the age of 18 fell by two percentage points. That pattern was echoed with both men and women, even while men skew younger than women.

The Census Bureau projects that this trend will continue for the next several decades. Even as the baby boom fades, America will remain more densely old than in years past, with enormous implications for the economy and our culture.

But that’s in the future. For now we can just enjoy the elegant presentation of an interesting set of data, as Star Wars’ Mr. Spock would have wanted.