On Aug. 20, the day Biden will accept the Democratic nomination in his bid to become the oldest occupant of the White House — he would be 78 days older on his first day in office than Ronald Reagan was on his last—it is worth holding the subject up to the light from both angles.

How old is Biden?

Well, he is older than 94 percent of all living Americans, and older than 96 percent of all people alive on the planet, according to demographic data compiled by the United Nations.

He is already older than 27 presidents were when they died — including 14 years older than Franklin D. Roosevelt and 13 years older than Lyndon B. Johnson.

When Biden arrived in the U.S. Senate at age 30 on Jan. 3, 1973, he joined six senators who were born in the late 1800s. Of those 100 people — all of them men, and only one not white — he is one of just 13 who are still alive today.

If he wins in November, he will be the only person to be president representing that historical seam between the “Greatest Generation” that fought World War II and the Baby Boom generation that has dominated national politics since the early 1990s.

Biden’s comparatively advanced age, however, is a useful lens for viewing the comparative youth of the country he hopes to lead. The life of a single person can bridge historical eras that seem more distant than they really are.

There are 329 million Americans alive now, and there are approximately 155 million Americans who have died since he was born on Nov. 20, 1942. Based on rough demographic estimates, Biden’s life has overlapped with well over 80 percent of the people who have ever lived in America since 1776.

Imagine that Joe Biden as an infant was bounced on the knee of someone who was the same age then that he is now. That person in turn was born early enough that he or she in theory could have bounced on the knee of Abraham Lincoln.

Albert Henry Woolson, the final documented veteran of the Civil War did not die (at age 106 in Duluth) until Biden was 13 years old, in 1956. Peter Mills, the last person reliably known to have been born into slavery did not die (at age 110 in Pittsburgh) until 1972, when Biden was in the closing weeks of his first Senate campaign.

Biden was born two years after Robert Zimmerman, not yet known as Bob Dylan, seven days before Jimi Hendrix, and two months before Janis Joplin. Unlike Hendrix and Joplin, Biden was not at Woodstock, and it is unlikely he was tempted to attend. By August 1969, he was already practicing law in Wilmington, Del., had been married for three years and was changing diapers on an infant son.

Perhaps these data points cry out for what journalists call a “so-what paragraph.” Here it is: Many icons of Baby Boomer culture, like Bob Dylan, were not actually Baby Boomers themselves, and neither is Biden. The Baby Boom generational cohort, according to standard demographic conventions, did not begin until Jan. 1, 1946. This means that Biden, if he wins, would be the only person in history to become president from a distinct generation of people who were too young to be in World War II but were already emphatically into adulthood by the time of Vietnam, and the political and cultural upheavals of the 1960s.

For four decades, from Dwight D. Eisenhower’s victory in 1952 and George H.W. Bush’s defeat in 1992, the presidency was occupied by eight men who had all, in different capacities, served in the military during World War II. After Bill Clinton’s victory in 1992, the White House has been held by four Baby Boomers, none of whom have had full-time military service. (Obama, born in 1961, was only 11 when U.S. military involvement ended in Vietnam, and likely has only loose identification with older Boomers.)

Until earlier this year, when Biden and Bernie Sanders — born three months before Pearl Harbor in 1941—were the last candidates standing for the Democratic nomination, it looked virtually certain the presidency would skip an entire generation.

In one sense, these generational boundaries are sociological conceits. Biden, after all, is just 43 months older than Trump, and 45 months older than Clinton. But those three-plus years have an outsize historical significance.

Have you ever studied old yearbook photos as they changed over the 1960s? Biden’s photograph in the 1965 University of Delaware looks like most of the young men of his class, and the 20 years before that: A smiling, genial fellow in jacket and tie, with neatly trimmed, well-combed hair. Within three or four years, those yearbook photos would show a cultural transformation underway among both sexes, reflected in long hair, beards and beaded necklaces — poses that reflected a defiant, individualistic ethos many of these graduates would carry with them over the next 50 years.

Sociologists have labeled the bloc of Americans who came of age after World War II but before the tumult of the 1960s the “Silent Generation.” As a politician, the voluble Biden was hardly known for silence (though his general election strategy during a pandemic involves talking far less than Trump). But he does in other ways represent classic Silent Generation values. This group put a premium on organizational responsibility. They respected establishment institutions and worked hard to follow the rules and rise within them. They did not issue bracing challenges to government, universities and business. That came with the huge surge of young people born just in the wake of Biden and his peers.

Among Democrats, the Silent Generation produced people who thrived serving presidents — like Leon Panetta and Robert Rubin, both born in 1938. Among women, it produced leaders who entered public life after first raising children — like Madeline Albright (1937) and Nancy Pelosi (1940). But this generation’s dutiful ethos never spawned a president.

This history suggests one opportunity for Biden if he becomes president. He could help revive functionality and respect for institutions he plainly reveres. By coincidence, the same year Biden came to Congress the Gallup Organization began measuring public confidence in major institutions. Over nearly five decades, nearly every institution — especially Congress and the presidency — has seen its standing with the public dramatically erode. The hazard is that Biden’s values will seem irrelevant or ineffectual in a political culture gravitating to young leaders like Alexandria Ocasio-Cortez, who shot to fame by defying institutional traditions and harnessing social media.

Biden was an adolescent before televisions in living rooms became commonplace, had been in the Senate for a decade before office computers arrived, and nearly a quarter-century before email. Instagram likely will never become second nature for him.

Biden’s trajectory also invites reflection on the optics of history: Are leaders becoming less capacious figures, or is that an illusion of time? Biden was born when dominating figures—FDR, Churchill—bestrode the world stage. He is offering himself nearly eight decades later not as larger than life but as ordinary Joe, a preeminently approachable man.

Biden’s life takes on epic stature primarily when viewed through the prism of tenure. As Senate historical data compiled by my colleague Matthew Choi reveals, Biden in 36 years as senator and eight as vice president (who breaks ties in the Senate) served with nearly 20 percent of the 1,984 people who have ever served in the Senate. His Senate colleagues stretch from Hubert Humphrey, Mike Mansfield (the longest-serving majority leader) and George McGovern at one end to Barack Obama and Hillary Clinton at the end.

This summer, marked by racial unrest and the reminder — underscored by Kamala Harris — that a woman has never been elected president or vice president, can in some moods produce despair: Can the United States ever really purge its historic inheritance of prejudice?

Biden’s career, however, is at once a reminder that things do change and that we haven’t really been immersed in the effort to change for all that long.

Nancy Landon Kassebaum — the Kansas Republican who was the first women elected to a full Senate term without having a husband who previously served in Congress—didn’t join Biden in the Senate until he had been there for five years. Today there are 26 women — 17 Democrats and nine Republicans — in that chamber.

Biden was 24 in the “long, hot summer” of urban racial riots of 1967. Martin Luther King Jr. was 13 when Biden was born and Biden was 25 when King died. Biden was 13 when Rosa Parks refused to give up her seat on the bus. Even after 36 years in the Senate, Biden had served with only three African Americans. That is how many are in the chamber today, a number that will drop to two if Biden and Harris win.

In his second inaugural address, Lincoln spoke of American slavery’s “two hundred and fifty years of unrequited toil” and warned fellow citizens that it could be God’s will that “every drop of blood drawn shall be paid by another drawn with the sword.” There is still a century to go before 250 years of slavery will be matched by 250 years of nonslavery.

Biden’s personal story is long, and he is trying to write himself into a national story that, one hopes, is still in its early chapters. He began his public career serving with people born in the 19th century. If he wins the presidency, he surely will have some young aides who will still be alive in the 22nd century.

His speech to the virtual convention Thursday evening is one more step in the long march of a politician shaped by decades of history to make himself the most influential person in contemporary America.