Thomas Jefferson was 33 when he became the principal penman behind the Declaration of Independence, America's founding document.

The Reverend Dr. Martin Luther King Jr was 34 when he delivered his "I Have a Dream" speech at the March on Washington, arguably America's greatest oration.

John F. Kennedy was 43 when he took the oath of office in January, 1961, and made history by becoming America's youngest-ever elected president. His predecessor, Dwight D. Eisenhower, had recently turned 70, and the former general was viewed as an elder, and elderly, statesman deserving of a well-earned retirement. As Kennedy proclaimed in an electrifying inaugural address, "the torch has been passed to a new generation".

Youth, energy and dynamism have long been qualities that Americans have celebrated in their leaders, which is partly why the age issue has loomed so large in the 2024 election. Only two presidents have entered the White House in their 70s. Donald Trump in 2017, and Joe Biden in 2021.

Since the end of the presidency of Barack Obama, who was 47 when he took his first oath of office, US politics has not only looked chaotic and unhinged, but tired and exhausted. American democracy has seemed more like an American gerontocracy.

It is not just presidential politics; travel up Pennsylvania Avenue from the White House to Capitol Hill — former Democratic House speaker Nancy Pelosi, who was instrumental in pressuring Biden to withdraw from the presidential race, was 82 when she relinquished the gavel. Her then-deputy, House Majority Leader Steny Hoyer, was a year older.

The former California senator Dianne Feinstein, who died in September 2023, had recently celebrated her 90th birthday. Senate Majority Leader Chuck Schumer, though sprightly by comparison, is in his early 70s.

Biden's decline has become plain and painful

On the Republican side, Mitch McConnell, the longest-serving Senate leader in history, is in his early 80s, and exhibiting clear signs of cognitive decline. For now, though, he remains the Senate minority leader, a role he intends to fulfil until a Republican conference in November finally chooses his successor.

In 2022, Iowa Senator Chuck Grassley won re-election for a six-year term at the ripe old age of 89.

The median age of lawmakers at the start of the 118th Senate was 65.3, the retirement age in many countries. That makes it the second oldest Senate in US history.

For Joe Biden, the age issue had become insuperable, and obviously impossible to reverse. Every day he sets a new record as the oldest incumbent of the White House. Though he said that only the Lord Almighty could convince him to quit, Father Time ended up with a decisive say.

Biden's decline has become plain, and painful, to see and hear. His stride is now more of a shuffle. His voice is often reduced to a whisper. Sentences trail off. Thoughts become incomprehensible. Each time he descends the steps of Air Force One, you wonder whether he will make it, unaided, to the bottom flight.

When I first saw Biden on the campaign four years ago in Iowa I was shocked even then by his decline. For his speech that day, he served up a messy word salad. Rambling anecdotes made no political points. Seeing a familiar face in the crowd would take him on a meandering journey down memory lane. Looking like a candidate who had done his dash, he came fourth in the first contest of that year's primary season.

In last month's catastrophic debate performance with Donald Trump, his waning was even more pronounced. From his halting entrance on stage to his brain freeze on a question about Medicare, his impairment could not be concealed. When he started arguing with Donald Trump about their respective golf handicaps, it was a sure sign that the time had come to retire from frontline politics and to spend more time on the putting green.

America's entrenched 'gerontocracy'

Back in 1984, as he sought re-election, Ronald Reagan had used humour to negate the age issue. "I am not going to exploit, for political purposes, the youth and inexperience of my opponent," he memorably joked during a televised debate with his Democratic opponent, Walter Mondale.

But Reagan was 73 at the time, and capable still of landing a knockout zinger. Biden's age problem had become a capability problem. It could not be camouflaged with comedy.

For all the talk of a generational shift, Kamala Harris, who will celebrate her 60th birthday just before election day, is at the older end of post-war presidential aspirants.

Bill Clinton was 46 when he won in 1992. Lyndon Baines Johnson was 55 on the day of Kennedy's assassination. Richard Nixon and Jimmy Carter were both 56 when they took their oaths of office. George W. Bush was 54.

However, so entrenched now is America's gerontocracy that even a 60-year-old would seem young.

Why is it that members of the Silent Generation (those, like Joe Biden, born between 1928 and 1946) and Baby Boomer generation (which includes those, like Donald Trump, whose birth certificates date from 1946-1964) have dominated for so long?

On the Republican side, the rise of Trump in 2016 eclipsed a new generation of conservative leaders, such as Florida Senator Marco Rubio, Texas Senator Ted Cruz, former South Carolina governor Nikki Haley and Florida Governor Ron DeSantis, all of whom were born in the 1970s.