One day about 15 years ago, scientist Dr Zvi Lanir received a letter that changed his mind-set and utterly revolutionised the way he lived.
The letter was from the Israeli Social Security service.
"It told me that I was now considered an old person and was entitled to a small pension every month."
Lanir was almost 68 at the time, and, he quips: "I said to myself 'I am not old! I am in the prime of my life! Why do they consider me old?'"
However, he recalls, "I acknowledged that I was no longer young. So what was I?"
The question sparked years of research which led to the conclusion that while, in the past generation or two, our hugely improved life expectancy has given us more years of life, this extra time should not just be 'added on to old age.' Instead, it should be viewed as an unprecedented opportunity to embark on a completely new and different phase of life.
Nobody, he observes, could argue with the fact that dramatically increased life expectancy is the single most disruptive change in western society.
On average we now live more than 30 years longer than we did in 1900, but, says Lanir, economies, governments, policymakers, employers and even our language itself has failed to keep pace with the enormity of this change. As a result, says Dr Lanir, who is an expert in the field of coping with disruptive change, we quite literally need a mind-set reboot to capitalise on the opportunity presented by this revolutionary shift.
'Old age' as a concept, he argues, has now reached its use-by date because living longer doesn't mean we've simply got more years to plough through.
Instead it should be accepted as a whole new period in human life, which he has dubbed The Age of Wisdom.
People who prepare themselves for this new age, he argues, will enjoy an active, wise and satisfying stage of life, which will enable them to delay 'old age' to their very last moments.
It's easy, and still very common, to view retirement as an opportunity for a long 'holiday', he acknowledges, but that's not necessarily a good thing, because the mind and the body need to be active.
"Like any other muscle in our body, the brain's elasticity requires training for its preservation," he says. "When you experience, feel, think and generally work it hard, its flexibility grows, and so its capacity and abilities improve. The more you use your brain, the more efficient its neurons become, and fewer are needed to perform a specific action.
"Even the functioning of the synapses improves. Increased activity enables the transmission of information between the neurons to be more efficient."
Meanwhile, physical exercise is necessary to oxygenate the brain.
For Lanir, who has recently turned 83, this quest was revelatory. The social security letter, he recalls, had forced him to reconsider his future.
A family history of dementia and high blood pressure, added to the fact that cancer treatment years previously had left him with just one kidney, meant a potentially short life expectancy. He was faced with a choice as to how he would live his life from then onwards.
"Should I think about myself as an old person, behave as an old person, become an old person?"
As we age, he argues, we actually have two 'ages'. "One is our chronological age, which is the age that is on our driving licence."
The other, he explains, is our functional age, which he defines as a combination of four personality elements - how we function physically, cognitively, psychologically and socially.
Everyone is weak in some elements and strong in others, he says, but getting these four elements right is crucial to stabilising our functional age - or even make it younger.
"When I started my journey 15 years ago, my physical function was very poor for many reasons," he recalls. "I went to my doctor and said I wanted to improve my physical health. I asked her to test me every three months."
From then on, the scientist changed the way he lived:
"I decided to reframe my mind-set and way of life in terms of my life after retirement age."
He stopped using his car. Instead he walked or cycled around his home city of Tel Aviv or used public transport.
He significantly increased his interaction with others, particularly with younger people. And although he had retired from his position as CEO of his company, he didn't actually leave.
"I acted as an advisor or mentor to the younger generation both in the company and outside of it, every day," says Lanir. He took up yoga and Pilates and started to breathe differently in order, he explains, "to bring oxygen not just to my brain but throughout my body".
He stopped consuming convenience foods. He ate slowly and with intention.
And he completely changed his outlook on living:
"I now do everything with intention. I live and feel every moment of my life. I am in the moment, absorbing the meaning of the moment."
After six months, his test results began to gradually improve. When he reached 80, he and his doctor conducted a review of his data over the 13 years.
The results showed that several areas of his physical function had improved. Others had not deteriorated, which was significant, given his advanced age.
The other three elements of his functional age, his cognitive, psychological and social health had also all improved.
"I became wiser and less dependent on other people," he recalls, adding that retirement is a golden opportunity, post-adulthood, to create a new, active phase of life. It's something, he believes, which can "be much more enjoyable and rewarding than adulthood".
"The Age of Wisdom comes after adulthood and pushes old age away into the last moments of life," he declares, adding that he recommends that people begin thinking about, and preparing for, The Age of Wisdom in their early sixties.
These day, he adds: "I am ageing but I am not old!"
The Wisdom Years : Unleashing Your Potential in Later Life by Zvi Lanir (Exisle Publishing) is out now, priced €11.50
⬤ Exercise Regularly
Regular exercise is important for the creation and release into the brain of BDNF - brain-derived neurotrophic factor. This protein plays a major role in the health and function of neurons, in preserving the brain's elasticity and in the creation of new brain cell. Physical exercise keeps the mind alert, stimulated and challenged - and acts as an antidote to our natural inclination as we age, to sink into a sedentary routine, an attitude which would retire our minds.
⬤ Form New Habits
When we retire, we can very easily slide into mindless, lazy habits which require very little willpower to maintain - watching TV endlessly, overeating and staying home rather than making the effort to get out and meet new people. If we continue such habits we will become 'old'.
Physical exercise can be a major trigger for changing our habits - so to make it a habit, "engineer" the circumstances to make it easy, obvious and natural. For instance, if you want to start your day with a run, try putting your running shoes and clothing next to the bed.
⬤ Find Happiness In the Little Things
Happiness can be found in the everyday: the first sip of morning coffee, a conversation with our spouse, having friends for dinner or playing with the grandchildren.
⬤ Eat Better
The unhealthy foods we consume hurt our brains as well as well as our bodies, says Dr Lanir. Some foods, for example, are more important for us as we get older, because they counteract the damage done to our aging bodies and minds by free radicals (chemicals created in oxygenated cells). Foods rich in antioxidants like vitamins C and E and selenium can block free radical activity, or at least slow it down.
⬤ Make conscious thinking a habit
When your mind starts wandering and you feel yourself getting stressed, tune in to your senses, and name your thoughts and insights.