Joe Biden, on the numbers, is anything but average.

At 81, he’s already taken the cake, as the oldest president to lace up his shoes for another run towards the Oval Office.

And sure, he’s not the oldest global leader, with Cameroon President Paul Biya – at 91 – taking that spot, but he is now more than the combined age of the French President and the current Prime Minister.

But his advanced years – and whether we like that term or not, his years are advanced – point to other numbers where he falls well outside the average.

The average American citizen is 38½ years old; that means Joe Biden is double the age of those he wants to represent for the next four years.

The average retirement age of an American is 65 (for men and 63 for women). By the end of Biden’s second term – if he gets there – he will be two decades older than the average US retiree.

He’s already beaten the life expectancy of his countrymen, and yet he’s out on the hustings shuffling, confusing words and with almost a frozen look on his face that’s beginning to look sad.

But this whole international discussion, after his embarrassing debate defeat, is not just about his age.

It’s about ageing.

Even a US president can’t escape that process, and in Biden’s case, according to many US American experts, the speed of his visible decline is accelerating.

And none of the rationale, coming from inside his camp or from the broader Democratic movement, is calming the jitters on show across the globe.

Is there a time, rather than an age, where the demands of an office mean a candidate should no longer be eligible?

It’s almost inconceivable that an 80-year-old – irrespective of their fitness – would win high political office in Australia.

Compulsory retirement is largely unlawful in many American jurisdictions, but there are exceptions. Pilots have to hand in their stripes at 65; air traffic controllers are retired to do it years earlier. Foreign service employees, firefighters and even judges in many states need to retire their work shoes at, or before the age of 70.

This isn’t because they’ve been labelled a number, like a bingo card. It’s because that’s the age when worker productivity significant declines.

But when it comes to the US presidency, it seems none of that applies. In the US, you can run the country until you are 100. Or even from a jail cell.

Joe Biden admits it is difficult to stay up with the gruelling pace of the presidency; that’s why he says he doesn’t want work commitments after 8pm. And surely we’ve all seen the evidence of that in the way he walks and talks?

His likely competitor Donald Trump is no spring chicken. He turned 78 last month, making this political duo the two oldest major-party candidates in American history to vie for the top office.

Whether you are a US citizen watching it at home, or an Australian interested in global affairs, that’s disheartening at best, and perhaps even a tad scary.

Thank goodness it’s a trend unlikely to catch on in Australia, where we are too quick to dismiss the wisdom and experience that comes after 50.

Whatever a birth certificate declares, we need leaders who are agile physically and cognitively. But we also need our politicians to understand the lives of the people they serve.

It’s a gripe in electorates the world over. Do they put petrol in their own cars? Know the price of a loaf of bread? Understand the parental anxiety of a child obsessed with their smart phone?

Perhaps Joe Biden might surprise us.

Perhaps he plays Minecraft with his grandchildren, who call him “pop”. Perhaps he is the first to “like” his granddaughters’ Snapchat posts?

Perhaps they call him with a dilemma; something many children, worried about the overreaction of their parents, reserve for their grandparents.

Perhaps he understands an American, a quarter of his age, who cannot find a job. Or how the future AI will mould for all of us.

But, on the shaky, faltering and frail performance we see, that’s hard to see.

It doesn’t make him any less of a person; but we should all want more of political leaders, no less the president of the US.