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My wife certainly likes asserting 50 is the new 40, while my children think 50 makes me as old as Methuselah.
But sometime in the future will come a time when I am not young.
It is impossible to tell when that might be - during this series on ageing in Dunedin I have met people in their 90s who are still firing on all cylinders, and people in their early 60s who require carers.
So when are you actually old?
And what should you do to be ready for that day?
It is a cliche, but you need to use it or else you will lose it, academic Debra Waters said.
"We know you peak in your bone and muscle capacity in your 20s and 30s and then you start a steady decline," the director of Gerontology Research at the University of Otago Department of Medicine said.
"If you don't do anything, if you are not physically active enough to slow that age-related decline, you will see a fairly precipitous loss which accelerates after the age of 70."
Researchers were now using the Dunedin Multidisciplinary Study to see if symptoms of decline doctors normally looked for in over 65s were also present in middle-aged people - and might then be able to be worked on.
"Surprisingly, muscle is quite a plastic organ and will respond even if you take quite a sedentary, frail obese person and put them into quite a rigorous exercise regime, they completely change their function and body composition," Dr Waters said.
"You can see quite profound changes in old age, so it's never too late to start - but it is better if you can maintain it throughout your lifetime so it is a behaviour and a habit that you stick with."
Regular moderate to vigorous exercise which got the heart working was good, but people also needed resistance training - pushing on the muscles hard enough so that they needed to respond and work.
"That's why fall prevention exercise classes do sit and stand exercises," Dr Waters said.
"It is a simple exercise, but the ability to stand out of a chair without pushing on their hands is for me one of the key indicators - that's a big red flag that they have serious lower body weakness."
Middle age was the danger time for people, as they stopped playing sport and cut back on active lifestyles, Dr Waters said.
"As you do less, it becomes harder to do anything and it becomes a downward spiral, so if you can maintain doing things you feel comfortable with and are safe ... it's a fine line between doing things and knowing your limitations."
Dr Waters is also one of the directors of the Ageing Well National Science Challenge's strategic advisory group, which has several research projects studying mental health, social isolation and old age.
"There is a tight correlation between physical and mental health - there is a growing body of evidence showing that people who stay physically fit have benefits to their mental capacity as well.
"There are also the social benefits of going out and doing things in groups - being outside and enjoying nature stimulates the brain as well as being good for the body.
Researchers are also looking at ways of staving off dementia, and have looked at whether the mind can be exercised like the body can.
Social isolation was another major issue, for both mental and physical wellbeing, Dr Waters said.
"That's why there are accredited aged care visiting services, and this is something which is also being researched in the national science challenge - we don't have the results yet but I would be surprised if that didn't have a positive effect on people.
"Once you get socially isolated, that normally doesn't have good health outcomes."
It is a cliche that you can't take money with you when you die, but it can certainly make the journey a great deal more comfortable.
For more than 20 years, the Office of the Retirement Commissioner has been pushing the message that New Zealanders are not saving enough for their old age.
For many in their target market it might well have been too late for them to have the comfortable retirement they wanted.
If you retire at 65, on average a man can expect to live until they are 91, while a woman's life expectancy is 94.
In big red letters, the www.sorted.org.nz website asks me if I have enough money saved to last me for 26 years?
Their online tool is more nuanced, but as a rough guide a 2015 study suggests a single person leading a no-frills lifestyle will need an income of $50,000-$80,000 a year and a couple wanting money to spend will need an income between $80,000 and $110,000 a year.
Multiply those numbers by 26 or 29, look at the number of zeroes on your calculator, and ponder.
The commissioner has divided retirement into three phases: Discovery (65-74), Endeavour (76-84) and Reflection (85+).
It is likely many people will discover they don't have enough money, will endeavour to make more, then reflect that they wish they had started saving earlier.