What is old?

I ask because Professor Mary Beard wants us to reclaim the word and rebrand it. She says we hear "old" and instantly imagine "the hunched old lady and gentleman on the road sign".

I agree. "Old" conjures up zimmer frames, walking sticks and non-spill cups. There is a whiff about the word, of decrepitude, muddle, fumble and feeble mindedness. Beige anoraks, elasticated waist-bands and shoes with Velcro fastenings are the uniform.

Who is "old" nowadays? Does old age arrive with the bus pass? People have to be 60 to get it. If they are women they are pensioners. Mary Beard will qualify within the year since she is 59. Helen Mirren would have qualified nine years ago; Judy Dench 19 years ago.

But we do not think of them as "old". They are exceptions, aren't they? They belong with 68-year-olds like Goldie Hawn, Cher, and Susan Sarandon. We look at Catherine Deneuve and Tina Turner and say with admiration: "You'd never guess they're in their seventies."

Why is that a compliment? asks Beard. What is so bad about looking 70 when you are 70? She calls this congratulation of youthful appearance in later years "one of the weirdest double thinks in our culture".

It is worse than that. Our society values only youth and youthful beauty - never mind it is impossible to hang on to the first; painful and expensive to try to retain the second. We enjoy longer lives than our ancestors yet instead of celebrating age as one of our greatest achievements we are ashamed of it. Every chemist shop has a wall of anti-ageing creams. Hairdressers offer styles to turn the clock back. Cosmetics promise to return that youthful glow. And then of course there is surgery.

And it is not just a youthful body that must be maintained. I am looking at the front page of a popular newspaper with a strap headline: "Anti-age your brain: the series you MUST read."

No wonder 60-plus people cringe when they are told they look their age. So can we re-brand "old"? Beard says it needs redefining as much as "black" or "queer" did. I could not agree more. After all, what did "black" tell us about the man or woman it purported to describe? Were they nice, generous, good honest? Did they have artistic talent, sporting prowess or think great thoughts?

"Black", like fat or ginger or queer, was a lazy term designed to categorise and diminish. It does not deserve the word description. "Old" is just as limited in its scope and just as damaging. It conjures up an image that is so frequently inaccurate as to render it pejorative.

I have a friend in his eighties who has been having knee problems, so is not moving as well as he did. He has white hair too. He also has a great intellect, is a fine writer and orator, has a comprehensive recall of historical fact and a well-rounded grasp of current affairs. Oh and he works every day of the week.

Is he "old"? In numerical years yes - not in any other way. Old does not begin to describe him or anyone else for that matter.

Consider the facts. It is only a few years since the abolition of the default retirement age yet more than one million people aged 65 plus are in work, according to figures released by the Department of Work and Pensions for International Older People's Day on October 1.

Almost half of the UK's 4.6million entrepreneurs are over 50 and of these 428,000 are over 65. This demographic change has crept up almost unnoticed partly because it gets harder to tell a person's age. If a man or woman is vigorous in their movements, trim, fit and in touch with what is going on in the world and inquiring, we consider them young or not old - because "old" as we know it does not define them.

It is just as well reality does not live down to our image of advancing years since, according to the 2011 census, Scotland now has more citizens over the age of 65 than under the age of 15. It is a first and in another decade many will still be working or be active in other ways.

Just yesterday we heard one of the 2014 winners of the Nobel Prize for Physiology or Medicine is John O'Keefe, of University College London. O'Keefe is described by a friend as a renaissance man - a neuroscientist and enthusiastic basketball player who probes the functions of the fundamental brain circuits and shoots hoops with Obama. He is 75 but his age tells us the number of years he has been on the planet. Nothing more.

Beard decries images of older people like the advertising picture for senior rail cards. It depicts Darby and Joan types setting off to see their grandchildren, rather than Professor Beard, the renowned classicist, on a regular work trip to London. Yet whereas in the last generation retired people tended to work as taxi drivers or builders, today they are management consultants, accountants, photographers, entrepreneurs - even rock stars.

But I come back to wondering what age group now qualifies as old? Should any? Last week we heard the Queen's birthday card team has taken on extra staff to cope with a 70 per cent rise in people reaching 100 in the past decade. There are currently 14,000 centenarians in the UK. But consider that, of babies born in 2012, it is expected one third will reach 100. So if 60 is the portal to what used to be considered old age, will people be old for 40 years - or almost half their life?

The Queen is an example of an 88-year-old still going strong. Does anyone look at her and think of the teetering couple on the road sign? We are not immortal. We do age. Beard suggests we celebrate the fact. She would like us to cheer for every year we defeat death and carry on being productive, creative and part of life.

In its present meaning "old" is nothing more than a lazy insult. It labels people as damaged goods, as past their sell-by date, as somehow pathetic when that simply is not the case. Terms like black and queer were revolutionised when ignorance was dispelled and when there was a popular will to change them. We have had a period when frail pensioners were herded into care homes and out of sight. They had no voice, no clout. They could not fight off being labelled. That has changed.

That meaning of "old" must too. I am hopeful it will.

The over-60s are a growing percentage of the population and increasingly they are staying physically and economically active and visible and vocal. They will be seen differently because they behave differently. They will be treated with respect because they will demand it.

Beard says she hopes that by the time she dies "old will be something that makes people fill with pride". I disagree. I hope the word is only used to reflect longevity.

I would always be more interested to hear how people used their time than how long they had lived. One word can't encapsulate that in the future any more than it does now.