Early Friday morning, Sen. Charles E. Grassley (R-Iowa) announced that he would, in fact, run for reelection next year. This had been a lingering question not because Grassley faces a significant primary challenge or was ensnared in scandal. Instead, it was a question because last week he turned 88 years old.

There are more 88-year-old Americans than you might expect. The most recent estimates compiled by the Census Bureau put the number at about 700,000 last year, a big chunk of the 6.7 million Americans who are aged 85 and over. There are also probably more 88-year-old Americans serving in the Senate than you might think. Grassley’s birthday brings the total to two: Sen. Dianne Feinstein (D-Calif.) hit that anniversary earlier this year.

In other words, 88-year-olds make up 0.2 percent of the U.S. population and 2 percent of the U.S. Senate.

There are some good reasons for members of Congress to skew older than the public in general. One is that children aren’t allowed to serve in the House or Senate, a prohibition that seems increasingly arbitrary with every passing week. The other, more important reason is that Americans are getting older, too.

You are probably familiar with a demographic phenomenon called the “baby boom.” From 1946 to 1964, Americans had a lot of children, creating a bulge in population totals that’s still obvious 75 years later. So, particularly over the past 20 years, there’s been an increase in the density of the population that’s aged 55 and over (since the oldest boomers hit 55 in 2001) and a corresponding surge in the age of members of Congress. (The data below rely heavily on FiveThirtyEight’s 2014 look at the age of members of Congress.)

Big surge in Americans aged 55 to 75; big surge in the number of members of Congress in that same age group.

There’s a word for this: gerontocracy. It means “government by older people,” in essence, and is often offered as a pejorative. But it’s also a simple reality in a population that is both skewing older and is projected to continue to skew older even in future decades.

Nor is it only a function of Congress. President Biden is the oldest president in American history, the first member of his generation to serve in that position. We’ve had four baby boomer presidents, though, including Bill Clinton, George W. Bush and Donald Trump, all of whom were born within two months of each in 1946, the first year of the boom.

You can see below how the increasing age of the baby boomers is pushing up the average age of members of the House and Senate.

Interestingly, the average age of Congress dipped slightly in 2019, after Democrats regained control of the House. A lot of those who retired or lost skewed older than the candidates who replaced them. This year, though, the average again shifted upward — as elected chambers filled with incumbents will tend to do on a year-over-year basis.

You may also be interested to know that, assuming no retirements or other changes to the Senate’s membership by next summer, there will still be only two senators who are 88. That’s because Sen. Richard C. Shelby (R-Ala.) will by then have reached that age as Feinstein hits 89. If Grassley is reelected in 2022 and serves his full term, he’ll be 95 by the time he’s up for reelection. If he runs again and wins again and serves out that term, he’ll be 101. And only then would he be the oldest actively serving member of the Senate, edging out former South Carolina senator Strom Thurmond.

Something to aim for.