We were at a memorial service, swarming outside a church in a conglomeration of people gathered around a shared loss.

'How lovely to see you again', an oldish man said, looming through the crowd. I smiled and searched for words that would console his confusing me with someone else.

Then something familiar caught my attention. The face of an old friend I hadn't seen for years asserted itself, like a blurred picture coming into focus. "How you've changed," was what I didn't say.

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It was a theme of the day. What fascinated me was the unequal force with which age had attacked the gathering. There were women for whom time had stood still; who looked 15 or 20 years younger than their years, without cosmetic assistance.

There were men in their sixties with that vigour of movement so characteristic of youth.

And there were others who'd crinkled and crumpled; who'd grown white haired or balded or bloated.

It was as if a river had run amongst us, gathering some into the flow and leaving others on the bank to enjoy the sunshine for longer. I was reminded of them yesterday when I read Joan Bakewell's formula for happiness in old age: "Give up ambition, rivalry and anxiety'.

But should we? And if we do, when?

Dame Joan is 81 and still going strong. The former tsar for older people was speaking last weekend at the Hay Literary Festival. She is a member of the House of Lords. She's clearly not taking her own advice.

That apart, is she right?

Let me echo her in recommending people of every age give up rivalry and anxiety if they want to be happy. But I'd suggest they hang on to ambition until it's torn from them by the grim reaper.

Of course she is right to imply there is more to life than a race up the greasy pole. But, to me, ambition isn't about that.

It is the impetus we all need to achieve something in life and to do it to the best of our ability. It is about personal development. And when you cease to develop, you shrivel.

Isn't the satisfaction that comes with achievement important in old age too?

I feel supported by advice from Harvard Medical School. In 2012 Dr Anne Fabiny, the assistant professor of medicine, came up with four recommendations for remaining mentally alert.

They are: to be a lifelong learner; to push yourself into mental challenges; to move out of your comfort zone into new surroundings; and, finally, to be social. Isolation depletes brain reserves. Physical exercise also belongs in the mix.

Isn't ambition at the core of that recipe? Surely we're being warned not to rest on our laurels? The zip needed to get ourselves up and out derives from the life force, from the determination to live as well as we can for as long as we can.

For an achiever such as Bakewell staying connected isn't difficult. She is still built into the system. She has a voice.

But, for many people, retirement from full-time work can be a social as well as a professional cut off point and it can happen decades before 80.

The daily ease of slotting in with colleagues vanishes. Income reduces and socialising is not top of the budget. There is a loss of identity. How does a man introduce himself when his profession or his work has defined him? How does a woman?

Saying you are retired will cause eyes to glaze over faster than saying you are a housewife.

So confidence shrivels a little. The retired find it easier to shirk the next party and the world spins on without them. It is all too easy to become isolated, lonely or depressed. Joan Bakewell says so too.

I would fear for a country like Scotland if pensioners took her advice. By 2031 Scotland will have almost 1.3 million citizens past working age with 650,000 of them aged over 75. That's a lot of people gazing at the sunset. It will put an unhealthy strain on the 2.96 million workforce unless many of those pensioners continue to generate an income.

Besides, how many will be able to afford an ever lengthening old age without work of some kind?

In 2012 more than 300,000 pensioners in the UK started their own business, a rise of 44% in 12 months. A further million opted to stay in employment beyond the age of 65. It is a grim reality for some but others relish the opportunity and the challenge.

Since we are staying healthier for longer, it's possible to pursue long- held dreams that duty didn't allow time for.

A new enthusiasm can be rejuvenating. Life can continue to be enriching in every sense. As old colleagues are shed, new acquaintances arrive.

I speak from experience. As I saw my bus-pass approach I returned to university to re-train. On campus I bumped into a clutch of contemporaries, each doing a different subject.

I won't claim that getting back to my books was easy but it has been one of the most stimulating and worthwhile things I have done.

I reckoned that, if Hillary Clinton was contemplating the presidency of the United States, I could think about a new career.

Has my brain density increased? Well, if there is a muscle in there it has been strained. I have been out of my comfort zone and I've encountered a whole swathe of new people of all ages.

Above all, I have been engaged and stimulated and busy, a part of the whirl of life.

I understand those of a more philosophical bent who feel they no longer need to look over the top of the next hill. They find a gentle mercy in learning to just be; in taking pleasure in the small things and the wonder of their natural surroundings.

I, too, have moments like that. But they are just moments. Perhaps as more decades pass they will stretch to days and weeks and months; perhaps not.

I'm afraid I see Bakewell's invitation to set aside ambition as a cul de sac. To me it is an invitation to elasticated waist bands, corn plasters; an invitation she delivered in blue silk and elegant drop earrings.

For me, the pleasure of remaining in lifelong learning, of having deadlines and of meeting interesting people all the time, is that truly I forget what age I am.

So, until creaks arrive and memory dims, I intend to carry on carrying on and enjoying every moment. I want to emulate Joan Bakewell by following her example.

She might talk about relaxing and letting it all go but, by most people's standards, she is still succeeding.

She has a job for life and an income with it. And she has the chutzpa to take to the national stage to chivvy the Government.

I'll hope to do as she does, not as she says. And I very much hope you'll join me.