The Queen is 80 this week and still at work. In any walk of life that is a handsome milestone and to reach it hale and hearty is a cause for celebration. To someone who has spent half a century in the same job it is the more remarkable.

Unlike a jubilee a birthday is a personal, not a state, anniversary but in the Queen’s case person and position are one and the same. Eighty is an age at which most people are not just on bus passes and free prescriptions, but feel their responses are slowing and life’s pleasures becoming more intimate. Corgis have more charm and secretaries of state less.

Yet Britain’s monarch shows no sign of tiring, let alone retiring. She may live free of the cares of ordinary mortals. She takes regular holidays and leaves the myriad concerns of daily life to be managed by others. Policies of the royal household she long ago resolved by opting for no change. When she is gone anything may go, so while she stays it may as well remain the same. The physics of the British monarchy is statics, not dynamics.

Yet the Queen’s stamina and equanimity are astonishing. Comfortable she may be but there are strains that nobody can delegate, not least those of her lively and problematic family. Nor does she let up. She put in 378 engagements last year, not far down on 466 in 1979, many of them on her feet and of bone-wearying, mind-draining boredom. She must eat, drink, converse and perform in public. She has just returned from bouncing round Australia and is off on a state visit to the Baltics.

While some duties are shifted onto other members of her family, she still treads the ceremonial round with no apparent diminution of energy. What at 70 was a bold assertion of monarchical staying power, at 80 is truly remarkable.

That the Queen does not “do retirement” is now a constitutional truism. She is known to take the view that hereditary monarchy comes table d’hôte, not buffet-style. It is about bloodline and is for life. Start picking, choosing, retiring, skipping generations or fiddling the rules and we lose the point. The monarch’s function is not to rule but to reign, not to decide but to dignify decision by her person. The function is performed as long as there is breath in her body.

Hence we must take the whole shebang of anointment, crown, orb, sceptre, allegiance, majesty and homage. We may regard them as the emperor’s clothes, but the clothes are bespoke and of a piece. Heredity may be an eccentric and indefensible basis for state headship in the 21st century but others are no better, mostly worse and certainly more dull.

The royal family has given Britain dignity, colour and more column inches of harmless diversion than would have come from any souped-up lord chancellor, Tory retread, Tony crony or whatever alternative we might find to don the cap of ceremony. Britain has an elected president already. Does it really want to see you-know-who and his wife sitting on the throne and decked in ermine?

Given that her mother lived to 101 the Queen is clearly in for the long haul. She will not retire and is most unlikely to precipitate an abdication by suddenly marrying a Roman Catholic or running off with a divorced American. Therefore the Prince of Wales must simply wait. We can only wish his mother all health and happiness and get used to the fact that British heads of state will, in future, be very senior citizens.

We should therefore make this a positive virtue. Forget the celebrity babies, the yummy mummies, the rock stars, the thirtysomethings, the menopausal baby boomers and their high-profile woes. Let us hear it instead for the under-represented elderly in British public life. The assumption that anyone over 60 is “bed-blocking” the Establishment or injecting gangrene into public discourse is outrageous.

The bias against age is a fetish that infects everything from politics to marketing to culture. It bears no relationship to intelligence, spending power or balance of population. Active voters over 50 dominate the polls, they watch more television, buy more books, form the majority of church-goers and visitors to galleries, museums, country houses and gardens. By 2020 a quarter of Britons will be over 65.

In the past four months it has been taken as read that a party leader under 40 is preferable to one over 60. This assumption would have baffled the ancients. What happened to wisdom or experience or institutional memory?

The idea that to be “the wrong side of 50” is somehow to be over the hill is not just an insult to medical science but also denies the vigour of millions of workers, which the economy desperately needs. They no longer do manual labour requiring physical strength. As life expectancy rises, brain power shows no sign of deteriorating after 60 while emotional stability and reliability, crucial to the new service economy, probably increase.

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