Tuesday is Donald Trump's 70th birthday. Happy birthday to Donald Trump. (Sorry we can't spend it with you.) Trump is one of only a handful of major-party presidential candidates to be a septuagenarian, a list that also includes John McCain in 2008 and Ronald Reagan during his 1984 reelection. But either way,  we're going to have one of the oldest new presidents in American history next year; Hillary Clinton turns 69 in October.

What's interesting about that bit of data is how it reflects the change in the U.S. population. If Trump had run as a 70-year-old in the year 1900, for example, he'd have been older than 98 percent of the American population. As it stands, he'll still be older than most — but 10 percent of the country will be older than he is. This is the graying of America, as you probably know. Both Trump and Clinton were born at the very front end of the baby boom, the post-World War II population surge that's now slipping into retirement age. Over the past century-plus, America's gotten bigger and older.

In 1960, John Kennedy was inaugurated as the youngest elected president in American history. At 43, he was older than 68 percent of the country. In 2008, Barack Obama was inaugurated at the age of 47 — four years older than Kennedy. But at that point, he was older than only 64 percent of a much-older country.

Prior to 1944, Census Bureau estimates of the number of people at each age aggregated everyone 75 and older into one category. (That aggregation is marked with a light gray bar in the graphs below.) By 1944, the aggregation point was 85. Recently, it's been 100 and higher.

How the age of inaugurated presidents compares with the population at large

Clinton and Trump's ages are for this year; acccompanying data is from the Census Bureau's 2015 vintage.

That's the good news for Trump and anyone else turning 70 or more in 2016. In 1900, when William McKinley won reelection to the presidency at age 58, there were about 207,000 people of that age, according to the Census Bureau. In 2015, the most recent year for which annual data is available, there were 2.5 million of them.

Obama was our first Gen X president. Our next president will be a throwback to the early baby boom. And if that president is Trump, he'll have gotten there thanks to a lot of votes from other members of his generation.