WASHINGTON (WASHINGTON POST) - When it comes to being a world leader, how old is too old? Voters in Malaysia will soon have to ponder that question, after the country's opposition alliance selected former prime minister Mahathir Mohamad to lead its challenge against Najib Razak.
At 92, Mahathir is almost three decades older than Najib. He was Malaysia's longest-serving prime minister, having held power from 1981 to 2003. If he wins the next election, scheduled to be held before August, Mahathir will become the world's oldest head of state or government.
Include hereditary rulers and autocratic leaders and that's quite a competitive title.
Britain's Queen Elizabeth II, 91, holds the distinction of being the oldest world leader - a title she took from Zimbabwe's Robert Mugabe when he was ousted from office last year at age 93.
Beji Caid Essebsi, Tunisia's 91-year-old president, is the oldest-serving elected world leader.
Mahathir's decision to run is a reflection of the state of Malaysian politics and, in particular, his public opposition to former ally Najib, who is linked to a multibillion-dollar financial scandal involving a state development fund.
If elected, Mahathir is expected to use his power to pardon another major opposition figure, Anwar Ibrahim, who is serving five years on sodomy charges that his supporters say are politically motivated.
If he is pardoned, 70-year-old Anwar could run for prime minister - potentially succeeding Mahathir, a former-ally-turned-rival-turned-ally-again.
At the same time, the Malaysian election fits into a global conversation about how old world leaders should be. That debate has been especially pronounced in the United States, where then-70-year-old Donald Trump faced off against 69-year-old Hillary Clinton in the 2016 election - the two oldest candidates in a US presidential election, with the exception of incumbent Ronald Reagan in 1985.
Some opponents of Trump contend that the president's age, in addition to a reportedly poor diet and limited exercise, have negatively affected his cognitive ability.
This idea has become resurgent amid accounts from the new book Fire and Fury by journalist Michael Wolff, that portray Trump as childish and unable to focus on the responsibilities of his office.
The White House has strongly pushed back against this idea, with Trump himself claiming to be a "very stable genius." It has also criticised as "ridiculous" those who raised questions about a speech by the president last month in which he appeared to slur his words - although, as The Washington Post noted at the time, Trump and his surrogates had repeatedly questioned Clinton's health during the campaign.
There certainly are benefits to having older leaders in office - they can draw on wisdom accrued over decades of high-level decision-making, as well as the accompanying support and name recognition. But there's no doubt that being a world leader also includes a workload and travel requirements that can be difficult for some older candidates to handle.
Looking globally, there have been a number of world leaders whose age appears to have affected their work. Before he was ousted, Mugabe was notorious for falling asleep during high-level meetings - when he was forced out of office last year, those leading the push to impeach him said his "advanced age" meant he was no longer physically able to run the government.
In the United States, Reagan's habit of forgetting things toward the end of his time in office led to public speculation about whether his mental health was deteriorating (after he left office Reagan was diagnosed with Alzheimer's, and his son later claimed that he had exhibited symptoms while in office).
However, age limits on heads of state or government are unusual. Instead, most countries tend to have some sort of minimum age requirement for running for office.
In many countries, this may be the same age as the voting age - 18 in many cases - although it can be higher. The US Constitution requires presidential candidates be at least 35. Even so, the world has seen a surge in younger leaders in recent years.
France's Emmanuel Macron entered office at 39, while North Korean leader and high-profile Trump foe Kim Jong Un is 34. The youngest world leader, Sebastian Kurz, was elected chancellor last year in Austria: at 31, he is just over one-third the age of Mahathir.
Few nations have any upper limit on the ages of their leaders. Indeed, when push comes to shove, the few limits there are can be strategically ignored - China's Xi Jinping, 63, is widely expected to flout Beijing's informal retirement age of 68 to continue for a third term - or outright repeal it, as happened in recent years in Turkmenistan and Uganda, by legal means.
Perhaps that's for the best. Experts generally agree that age alone can't determine someone's health or ability to work. Last year, Mahathir gave an interview to The Straits Times in which he explained that the secret to his youthful looks (the newspaper noted that his appearance had changed little in 12 years) was simple: Don't overeat.
But Malaysian voters' worry may not be that Mahathir has changed too much, but that he has not changed enough.
During his 22 years in office, Mahathir had a fearsome reputation as an authoritarian with little time for liberal values, with his tactics paving the way for Najib. And despite his age, Mahathir has expressed little regret for his alleged past excesses since reentering politics last year.