Nikki Haley should have joined the circus, because she is great at walking a tightrope. Ever since she left her position as Donald Trump’s ambassador to the UN in 2018, Haley has kept on the right side of the former president, while simultaneously keeping a safe distance from Trumpism. She has criticised Trump just enough that she can cut ties with him should he become a liability; she has also backed him just enough to count him as an ally should he prove useful. Haley, who is expected to run for the Republican presidential nomination in 2024, alternates between throwing red meat to Trump’s base and keeping one foot in polite society. Hers is a very polished populism.

Haley’s balancing act was on full display last week, during an interview with the Christian Broadcasting Network, during which she was asked about the mental health of Joe Biden. Haley cannily avoided commenting directly on Biden, who turns 79 this month, but did make pointed remarks about the need for cognitive tests for ageing politicians. She was rude under the guise of reasonableness.

“Let’s face it, we’ve got a lot of people in leadership positions that are old,” Haley said. “That’s a fact … this shouldn’t be partisan. We should seriously be looking at the ages of the people that are running our country and understand if that’s what we want.”

Buried within the ageism, Haley has a point. Biden is the oldest sitting president in US history. Meanwhile, the current US Senate is the oldest in history, with an average age of 64.3 years. Dianne Feinstein, the oldest senator, is 88 and has held her California seat since 1992. She is closely followed by the Iowa senator Chuck Grassley, also 88, who has been in his job for four decades. Six senators are at least 80; 23 are in their 70s.

There is nothing wrong with politicians being in their 70s or 80s. Experience can be an important asset, and, while we tend to associate youth with energy and innovative thinking, some of the oldest politicians in the US have the most dynamic ideas. Senator Ed Markey, 75, co-sponsored the green new deal. Bernie Sanders, 80, captured young people’s passion like no other US politician in recent years – as did Jeremy Corbyn, 72, in the UK. Meanwhile, fresh-faced Pete Buttigieg, 39, whose 2020 ambitions made him the first competitive millennial presidential candidate, ran on stale ideas. He is a McKinsey millennial, whose status quo platform resonates better with older voters than with his peers. You can sell out at any age.

That said, it is worth asking if there is a reason why US leadership skews so old, particularly as the US is an outlier among the countries in the Organisation for Economic Co-operation and Development (OECD) in this respect. The New York Times noted last year that the average OECD leader is almost 25 years younger than Biden. Again, while it is good to have politicians above retirement age – there is a problem if it is because the political structure is making it hard for a new generation to rise to the top.

The US system massively favours incumbents: members of the US Congress are typically re-elected about 90% of the time. That breeds complacency. It can also breed myopia. Barack Obama, for example, has admitted that fundraising for his 2004 Senate campaign made him more like his wealthy donors: “I spent more and more of my time above the fray, outside the world of immediate hunger, disappointment, fear, irrationality and frequent hardship of the other 99% … I suspect this is true for every senator: the longer you are a senator, the narrower the scope of your interactions.”

Ultimately, it is not the age of our politicians we need to worry about. What matters is having a government that represents the people it serves. Age limits won’t solve that, nor will cognitive tests, but reassessing our ideas about leadership might. Truly great leaders are not the people who cling to power the longest; they are the ones willing to pass the baton to a new generation.

• Arwa Mahdawi is a Guardian columnist