We are used to Prince Charles's old-fashioned ways.

But now he has adopted an old-fashioned lifespan. "I'll run out of time soon. I shall have snuffed it if I'm not careful," he said just before his 64th birthday.

Run out of time when he has just turned 64? Snuffed it? I hope he saw the pictures of Mick Jagger strutting his stuff on Sunday night. The 69-year-old rocker left an audience of 20,000 at London's O2 with lots of satisfaction. One delighted fan said Jagger "must have covered several miles" during the 50th anniversary concert.

Loading article content

It is time Prince Charles got modern, in this at least. He will be king so his attitude matters, especially when it comes to ageing. You see he'll be the king of the baby boomers – the generation that will be the longest lived in the history of mankind. We've set new trends all through our lives and this is the latest one. As always we are lucky. But this stroke of luck presents us with a challenge, one that too many people in their 50s and 60s still haven't understood.

The life expectancy of the average Scottish man is now 75.9. For a woman it's 80.4. (You can add more than two years to both for the English.) If you subtract from the average the smokers and drinkers and those who have the misfortune to suffer ill health, there are a lot of nonagenarians and centenarians left.

There is every chance the Prince will be among them. Given that the Queen is going strong at 86; that the Duke of Edinburgh is still twinkling in his 90s and that Charles's grandmother lived until 101, he may still have one-third of his life ahead.

Chances are many people his age do too. But what is an unmitigated opportunity for Prince Charles is a financial and occupational challenge for the rest of us. When he becomes king his daily diary will read like a rest cure compared to now. We know he writes and paints and travels and farms and gardens. We all know about the great achievements of the Prince's Trust. I didn't know until I looked at his website that he has about 16 charities. Ironically, given his attitude, one is Mature Enterprise. It supports people over 50 who – faced with unemployment or redundancy – want to start their own business.

The website carries case histories of people relishing the plunge into entrepreneurship after a career as an employee. People are converting hobbies and passions into money-making enterprises. One has a flower-growing business, another makes leather cases, another runs computer lessons for seniors. From knitting to adult education to law research, the over-50s have been turning their lives around.

They have been becoming wealth creators and they have been doing it with the help and support of the Prince. But instead of blowing his own trumpet, instead of demonstrating that he too is grasping new opportunities, his joke made him sound like an extra in Last of the Summer Wine. It is important because this reinventing ourselves is what all but the most affluent baby boomers need to achieve. (And even the wealthy would be happier keeping busy.)

The challenge is that most of us won't be able to continue our first careers but we don't have large enough pensions to sustain us in reasonable comfort for several more decades. Ergo most of us need to address the matter.

Future generations will have time to adjust to their third age. They'll be able to plan for it, the same way they planned for their education. But it is upon us – and the welfare state that spoon-fed us through our early years can't cope. So it's a challenge that is both scary and exhilarating. But it is one we can't ignore.

We should remember that extra time is also a privilege. We are fitter for longer and technology means physical infirmity needn't be as great a bar as it was: just look at stroke victim Hilary Devey on Dragons' Den.

Nor is it just about money. Involvement in life and maintaining interests are necessary for fulfilment, and help us to sustain a healthier life for longer. Viktor Frankl, the psychologist and writer who survived the holocaust, wrote in his book, Man's Search for Meaning, that when a man knows the why for his existence he will be able to bear almost any how.

His experiences convinced him that mental health was based on the tension between what we have already achieved and what we still ought to accomplish. He is thought to have coined the term "Sunday neurosis" to describe an anxiety at the emptiness of life after a working week.

It's a familiar sensation. This greatest of blessings, an extended lifespan, could become a curse if we prepare for death too early. If, in only our 60s, we pack away our abilities and ambitions and sit, dependently, waiting for the final trumpet, how bored and miserable will we be?

When my mother lived to be 102 I realised the need to plan ahead so I am back at university part-time. Like thousands of others, I've found the experience challenging and stimulating. It opens up new ways of thinking and dusts out long-neglected parts of the brain. It's enlivening to work through new ideas with bright people of all ages and from many ethnicities. I find myself arriving for the day feeling worn out and leaving six hours later, re-energised. And in between, the last thing on my mind is my own mortality – because the last thing on my mind is me.

The excitement of new learning, the challenges of setting up a business, the fun of fully living life while you are living, is the message Prince Charles needs to get across.

Those 16 charities, the books, the villages, the painting and writing all suggest it's the way he lives. Though he has more money than he could ever spend, he works. He wrings the last drop from every day. That's good. It's good that he is impatient to get on.

It is a great way to be but not because he will soon run out of time. Life isn't a race against the clock, it is a gift to be celebrated, a rock'n'roll rollercoaster whose ending should catch us in mid-flight, not sitting waiting with our aspirations, ambitions, dreams and unrealised talents packed away years in advance.