Age is a circumstance about which a person can do nothing. The appointment of Gabriel Attal as the Prime Minister of France has attracted much comment on the basis of his youth. At 34, Mr Attal has been positioned to do great things in his tenure in Hôtel Matignon, perhaps a stepping stone on a journey ending in the Élysée Palace, as President. However, he cannot change his age.

He is not so young that he is completely out of kilter with other world leaders, past and present. Sanna Marin became Finnish Prime Minister at the same age, 34. Rishi Sunak led the UK at 42. Humza Yousaf made it to Bute House at 37. JFK was 43, and that was in an era where young leaders were far less fashionable than they are today.

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Nonetheless, it is important to reflect on the age of politicians; what is the "right" age to be a leader? I have some micro experience of being young in politics. I was far from real power, as head of communications for the small Scottish Conservative Party at 25, but nonetheless I had a lot of clout in that arena. At the time, of course, I thought I was good at it. But that’s the thing about being young - you’re not old enough to know what you don’t know.

With hindsight, of course I was too young and too inexperienced to do that job. The second of those - experience - is the most important. You can, in theory, be 25 and have more life experience than a 35-year-old or even a 45-year-old. However, it stands to reason that the older you are, the more likely you are to have the sort of life experience that a successful leader needs to have.

Mr Attal attended one of Paris’s leading private schools, then went to university to study law, first, before completing a masters degree. He immediately became a political advisor, then a member of France’s National Assembly, then a government minister, and now Prime Minister. He is the dictionary definition of a career politician. This does not eliminate the possibility of him doing a good job; indeed, as I wrote on these pages last week, there is room in politics for people who are ideologically driven and who are in politics to think big thoughts and make major changes rather than to help the constituent who has a pothole at the end of her road.

However, there is little doubt that politicians are likely to make good decisions if they have lived experience of the areas on which they are presiding. This does not mean that every education secretary must either be a parent or a teacher, or that every health secretary has to have been a patient or a doctor. It does not mean that every transport minister must get the bus to work or that every housing minister must have experienced the difficulties in getting a mortgage or insulating a house. And it does not mean that every finance and economy secretary has to have worked in the private, public and charity sectors. But it would be helpful if our leaders and their cabinets had at least some of this experience, so that they could come together and be as representative as possible of their electorate.

This is an issue that, here in Scotland, we need to keep an eye on. On both sides of our constitutional debate, we experienced massive engagement by younger people. Teenagers became politicised, stayed politicised, got involved with their chosen political party and, in many cases, now find themselves in Parliament. A few have their hands firmly on the levers of power.

The Herald: Sanna Marin became Finnish PM at 34, Humza Yousaf reached Bute House at 37Sanna Marin became Finnish PM at 34, Humza Yousaf reached Bute House at 37 (Image: PA)

Some of them, despite their age, do have experience of the areas I mentioned:  healthcare, education, transport, housing, the economy. Others, though, do not. Others base their political actions largely on the writings of their favourite political philosophers rather than on their own life experience. Others make decisions about the world they imagine rather than the one they actually live in.

There is another end of the scale, of course, which is likely to come into sharp focus this year. President Joe Biden was first elected at 78 and, if he is re-elected this November, will be 86 at the time of his departure from office. His likely opponent, former President Donald Trump, seems positively youthful in comparison, but will himself be 78 when the election comes around.

One could very fairly argue that, even in their prime, neither of these men would have made a good President. However, on the basis that the world has to have one of them, we would surely rather they were two or three decades younger.

This is as much about science as it is about anything else. Other than memory, which slowly disappears from the moment we become adults, all other cognitive characteristics have a clear peak. Comprehension - perhaps the most important for a politician - reaches its peak in our 40s. A 20-year-old has roughly the same cognitive ability, in most areas, as an 80-year-old.

This is, it should go without saying, not an argument for all politicians to be in their forties. Politics is a unique industry. Politicians need not leap an academic hurdle, nor do they require qualifications. They do not need to be good, they just need to be picked. And they do not need to be successful; there are no key performance indicators nor an annual appraisal. They are there at the behest of the people who elect them.

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This is precisely how it should be. Being a politician is not a normal job.

However, we should all want our politicians to be life-experienced. We should want them to see the things we see, to do the things we do, to understand the things we understand, before they are put in a position of making decisions about them.

This takes an introspection which does not come naturally to young people. It is not a facet I possessed in my early twenties. But it is something on which I occasionally give advice, when asked, by young political staffers at the Scottish Parliament.

I understand their obsession with politics. I had it then, and I still have it today. I understand their desire to be elected (very occasionally, I still get a twinge). But my advice to them is always the same.

Get out for a while. Politics will always be here, and you’ll be much better at it once you’ve lived some more life. Politics begins at 40.