Shadow cabinet colleagues of Jeremy Corbyn have been quoted as saying they are worried that he is too old to become Prime Minister.

The Mail Online quotes an unnamed shadow minister as saying: “A leader standing at a general election has to commit to doing a full five years. Jeremy is in good shape, but by May 2027 he will be nearly 78.”

The Independent also ran a similar story, using the same quote. And the Indy reports that a second “senior frontbencher” told them: “Jeremy has a lot of energy now. But 2022 is a long time away, let alone 2027.”

We don’t know who the journalists’ sources are, but taken at face value, the stories suggest two shadow cabinet members have doubts about their leader’s ability to govern effectively in his 70s. How unusual would it be to have a PM of that age?

Oldest first-timer

This whole story hinges on the assumption that a) there won’t be a general election until May 2022 and that b) Labour will win. Obviously neither of these things is certain.

Let’s assume they both happen. Jeremy Corbyn would be three weeks shy of his 73rd birthday if the election is held on 5 May, the date scheduled under the Fixed-term Parliaments Act 2011.

If Labour served a full five years, it follows that he would be nearly 78 at the end of his first term in office.

A victory on that day would make Corbyn the oldest Prime Minister to take office for the first time.

His closest rival is Lord Palmerston, who first became PM in 1855 at the age of 70, after a distinguished ministerial career.

Not (quite) the oldest to serve

Corbyn would not be the oldest person ever to hold the office of Prime Minister.

Gladstone (above) became PM for the fourth time in 1892 at the age of 82, and was 84 when he finally left office.

Churchill returned to Downing Street in 1951, a month before his 77th birthday, and only retired at the age of 80.

Still, if Jeremy Corbyn left office in 2027, he would be the third oldest Prime Minister since the office effectively began in 1721, and considerably older than average. The median age for all first-time PMs is 53. In the 20th and 21st centuries it’s 56.

Of course people are living longer now, and working longer, and staying healthier for longer, so it may be unfair to compare the abilities of a modern 72-year-old with someone of the same age in past centuries.

Mr Corbyn’s spokesman gave a statement today saying:

“Jeremy is extremely energetic, works extremely long hours and since he has been doing this job has performed at an extremely effective and high level.

“He is extremely vigorous. He has become more effective as a leader since he was first elected. I see no sign whatsoever that his age is an impediment to continuing to be leader.”

Oldest chancellor

If Labour wins in 2022, and current shadow chancellor John McDonnell is still in post, he will become the oldest politician ever to take office as Chancellor of the Exchequer of the United Kingdom – the job usually considered second in importance after the Prime Minister.

McDonnell will be 70 years and nearly eight months old, making him the oldest man to begin a term as chancellor.

Gladstone comes second, serving as chancellor (for the fourth time) at the age of 70 years and nearly four months in 1880. He held the offices of both Chancellor and Prime Minister at the same time, as was common in the 19th century.