We are living longer and more healthily than ever before – in spite of all the bugs that seem to lurk inside the NHS. Indeed, there are now more pensioners than children and octogenarians are two a penny – and becoming ever more plentiful.

It's an old folks' world now, though Miss Scott may not
think so.

Yet, paradoxically, the profession of politics is becoming younger. You might reasonably have thought that a job which, above all others, requires judgment, would be ageing with the population.

Experience does not necessarily improve judgment if the
individual was born without it,
but it usually helps.

William Ewart Gladstone remains a phenomenon. He formed the last of his four governments at the age of 82 and led it for another four years. During the 20th century, only Winston Churchill came anywhere near that. He was 81 when he resigned for the last time, utterly spent, in 1955.

Since then, things have been going downhill, at least in terms of age. Our last 10 Prime Ministers were, on average, 54 when they led their parties into government. Tony Blair and John Major, aged 43 and 47 respectively when they went to No 10, brought the average
down, and unless Gordon Brown can invoke divine intervention, David Cameron will reduce it further, beating Blair by a few months.

So, it is actually a young man's – or, perhaps more realistically, a young woman's – world. Sarah Palin, the 44-year-old modern equivalent of Annie (get your gun) Oakley, makes the point with her selection as John McCain's Republican running mate in the US presidential election. I am pre-occupied this week with age because that is what the US is going to be for the next three months. Since Barack Obama and McCain are neck and neck in the polls – and Americans, therefore, not apparently inclined to hold George W Bush against McCain – they have a lot of thinking to do.

Who is too big a risk in this dangerous world? Old man McCain, aged 73, with a relatively inexperienced go-getting girl as his running mate? Or Obama, 47, with Senator Joe Biden, the experienced 67-year-old foreign affairs specialist as his candidate for vice-president?

It is a very nice question for Americans if they can keep out of it Obama's mixed race, Biden's failure twice to win the Democrat nomination, McCain's failure to win the Republican nomination in 2000 – are they both losers? – and Palin's backwoodswomanship. In practice, they have a lot to ponder. But they will keep coming back to what George Bush Senior would describe as "this age thing".

Are you too old at 73 to become the most powerful man in the world and leader of the democracies, when Russia is intent on playing it rough and China is on the march? Or are you too young at 48, as Obama would be by the time of his inauguration, when you yourself, as distinct from your running mate, know little first hand of world affairs?

All this raises four subsidiary questions: is the top man a commander, does he know what he is doing, has he a coherent philosophy and is he healthy?

I don't think either is a Ronald Reagan, who resolutely steered his ship by a limited number of stars. McCain, with his impressive naval background, was born to command and I suspect that he sways much less with the wind than Obama, though it worries me that both seem to be as barmy as Al Gore about global warming.

In other words, McCain seems to be made of the sterner strategic stuff, but will he remain fit, and, if he kicks the bucket, will Americans feel safe in the hands of their first (young and very presentable) female President?

You can't get away from this age thing. I saw Reagan operating for eight years into his late 70s. He was not a bundle of energy. He had a short span of attention. But he was secure in his philosophy. He could delegate and he restored America's self-confidence before he succumbed to Alzheimer's.

So, it comes down to beliefs, consistency, strength of purpose and health. A vigorous young ditherer is as bad as a gaga statesman. Take your pick.