Too old or very wise: U.S. leaders are among the world's oldest. Is it a problem?

Age is something that does not matter, the Spanish movie director Luis Bu?uel once remarked. Unless, he added, you are a cheese.

But what about being sharp and spry and in your prime if you're a world leader or key lawmaker?

Globally, presidents and prime ministers range in age from 36 (Ibrahim Traoré, Burkina Faso) to 91 (Paul Biya, Cameroon), according to the Washington-based Pew Research Center, which describes itself as a "fact tank."

However, most world leaders are in their 50s and 60s. And women leaders tend to be younger than their male counterparts. Finland's recently departed prime minister, Sanna Marin, was just 34 when she took office.

But outside of the U.S., older leaders tend to be a feature of countries less free politically, according to Freedom House, a Washington research organization. This is a characterization that applies chiefly to despots and authoritarian types; dictators who engineer their systems to stay in power for far longer than democracy typically allows. Russian President Vladimir Putin is 71, Recep Tayyip Erdo?an of Turkey, 70. China's Xi Jinping, is 71.

At 81, President Joe Biden is not only the first octogenarian in the Oval Office, his relative seniority puts him among the 5% of world leaders who are in their 80s, according to Pew. Donald Trump, his rival for the presidency, is not far behind, at 78. Mitch McConnell, the Republican leader of the Senate, whose apparent health problems have been on public display, is 82.

How old is Mitch McConnell?: Senator's age under spotlight in increasingly old Congress

In the 118th Congress, the median age of House lawmakers, according to Pew, dipped slightly to 57.9 years, down from 58.9 years in the 117th. But the Senate's median age continues to rise. It's now at 65.3 years. Four years ago, it was 62.4 years. Throughout the 1980s, most U.S. lawmakers in Washington were in their 50s.

Biden, Trump, McConnell: united in their dotage

The U.S. is one of only two countries that Freedom House classifies as "free" with a leader in their 80s or older.

Freedom House rates people's access to things such as political rights and civil liberties. In its most recent "Global Freedom Scores," the U.S. pulled in a respectable 83 out of 100. Not as good as Canada and the Scandinavian countries, which were in touching distance of a perfect score. Not as bad as Afghanistan.

Steven Webster, a professor at Indiana University who studies U.S. political behavior and public opinion, said that it's clear that there is a "mismatch" between the median age of the U.S. population, which is 39, and the politicians who represent them. He said this could be explained in different ways.

One of these explanations is that members of Congress are staying in office for longer than ever before. Another is that Americans seem to favor incumbents. Once someone gets elected, they tend to stay elected. Another is that older adults tend to vote more than younger ones and in doing so vote for people closer to their age.

"Americans by and large are dissatisfied with Congress, but reelection rates are astronomically high. Yet we tend to vote for who we know, and who we know is older politicians," he said.

Physically and mentally fit

Biden has no major medical problems. He doesn't drink or smoke. He appears to exercise regularly.

Trump's doctors have repeatedly said he is in good health, though some physicians have noted if he has a Body Mass Index in excess of 30, he would be considered clinically obese.

McConnell's doctors have said he is not suffering from a “seizure disorder,” stroke or a “movement disorder such as Parkinson’s disease” despite two recent "freezes" in front of reporters.

Still, it’s one of the FBI and CIA’s biggest nightmares, now that those entrusted with the nation’s most sensitive secrets are getting older or could have medical conditions that could result in them blurting out classified information that could be used against America by its adversaries.

Larry Pfeiffer, a former senior CIA, National Security Agency and White House intelligence official, said he did not want to discuss specific individuals.

But generally speaking, he said, “For employees of the U.S. intelligence Community, mental fitness is one of the key components used in adjudicating whether someone should have access to our most sensitive information.”

“If an employee were suspected of suffering from dementia or other diminishment of mental faculties, depending on the severity their access would be suspended until a medical professional could reevaluate their fitness,” Pfeiffer said. “In some cases, remediation may be possible,” Pfeiffer added, “but in others there is no other remedy than a medical separation from service.”

Unlike intelligence officials, members of Congress get access to classified material by virtue of their being elected to office. As such, without any kind of adjudication, the intelligence community “has relied on the collective wisdom of senior leadership,” Pfeiffer said, “to determine when a member should no longer have the greater access afforded by membership on the intelligence committees.”

A system that requires 'massive amounts of money'

A poll from The Associated Press-NORC Center for Public Affairs Research found that 77% of those surveyed ? 89% of Republicans, 69% of Democrats ? think Biden is too old to be effective for four more years.

These views held across age groups, not just among the young.

Despite being just three years younger than Biden, there was less concern about Trump's age. (Other concerns were raised about Trump.)

Trump's big lead: Among nonvoters, many agree with him that elections are rigged

Stefan Lehne, a senior fellow at the Carnegie Europe think tank in Brussels, said that many countries in Europe have "fragmented political scenes" that allow for new parties to form relatively easily. This contrasts with the more or less stable two-party system in the U.S. of Republicans and Democrats.

Often these European parties are driven by charismatic, younger politicians who can rise to the top quickly. This is partly what accounts for the rise of far-right and far-left parties in Europe in recent years, whose leaders skew younger. The median age of a head of government in Europe, according to a Bloomberg analysis, is 53.

Lehne said a major factor driving the divergence in age between U.S. and European leaders is, well, money.

He said to get elected to the highest U.S. office requires "massive amounts of money and so therefore there is a political party preference for people who have a high degree of name recognition who are well established because nobody wants to invest in people who have little chance to get to the top."

This, he said, generally favors a ruling political class in the U.S. that has taken a lot of turns around the Sun.

"In most European countries you don't need to raise millions of dollars from private donors to run for office."

Lehne is from Austria. In 2017, his fellow Austrian Sebastian Kurz became the world’s youngest head of government and the first millennial to lead a European country. He was 31.

Narrowing the age gap

Phil Keisling is a former Oregon secretary of state who runs an organization named Vote at Home.

It aims to improve vote-at-home options at the state and local levels.

Keisling said that in order for the U.S. to narrow the age gap between voters and its elected officials, it needs to do more to encourage younger voters to participate in the political process.

This is something that is broadly true right across the world.

But Keisling said it was especially true for the U.S. political party primary votes, which determine who gets to be nominated as a presidential candidate. He said the median age voting age in these contests is 62.

And that those aged 18 to 34 barely vote in the primaries at all.

However, Keisling cautioned over placing too much store in age to address the U.S.'s political challenges.

"The problem of how old our politicians are in America is far less of an issue than how feckless and hyper-partisan they've become," he said. "I'm not sure changing the ages in a big way will cause our politics to be better."

Contributing: Josh Meyer

This article originally appeared on USA TODAY: How Biden's age compares to other world leaders