I can slide my hands under the soles of my feet without bending my knees. I can hold a plank for more than a minute, run for a bus (and catch it), stand on my head - and very, very nearly do the splits.

And yet, 18 months ago, I couldn't paint my own toenails.

What makes this transformation even more remarkable is that it was triggered after I turned 50, just when I imagined it was too late to change the course of my oil tanker of a body.

As I contemplated my sixth decade, I was heading for elasticated trousers, baggy sweaters and the inevitable health threats that go along with inaction.

Then I discovered yoga, which led to regular swimming. Walking helped me lose more than 12kg and has given me extra energy and less anxiety.

Now, Norwegian scientists have discovered that, as a recent adopter of exercise, I may have halved the chance of having a stroke. In fact, late bloomers - those in their 50s - have better health prospects than anyone who was once fit but has now stopped exercising.

Although the study focused only on men, lead researcher Erik Prestgaard says he believes the findings probably also apply to women.

The last 10 years have been filled with work, motherhood and some ill health - there wasn't time for exercise.

The running never happened, the gym memberships were cancelled and the new bicycle slowly rusted without a turn of the wheel.

The more inactive I became, the larger I grew and the less zip I had. On the rare occasion I did take to the road, my hips, knees and ankles were incensed.

But, last year, encouraged by a modest weight loss through a healthier diet, I made what was to become my final resolution.

In 2010, I had been diagnosed with breast cancer and, as a women's magazine journalist, I was familiar with the warning stories about obesity and lack of exercise.

I knew if I didn't grab this second chance of health in my 50s, I would never, ever change. And so I did.

Yoga seemed to me the way to go.

As well as making me more flexible, it promised to make me more mindful. Plus it was not as demanding as a session in the gym. (I've found out that it can be every bit as tough, but ignorance drove me on.)

I was shy about public Lycra- wearing and not knowing my crow from my lizard, so I looked for an online yoga course and found free videos that demanded no more of me than 30 minutes a day.

After that first month, I was hooked. With every session, the moves became easier and my stamina improved.

One day, I ran up a flight of stairs and found I could still breathe. My feeble wrists strengthened to allow me to hold a downward dog without pain.

Each day, after a brief shavasana - the best bit, where you lie on your back when the exertions are over - I would shower, roll up my mat and head to work with a newfound bounce to my step.

One month in, I was ready for a public yoga class. Eighteen months on, I am still practising at least three times a week - I have even taken my mat on holiday.

Yoga has led to walking and swimming and an all-round feeling of well-being. Last year, I did a walking half-marathon to raise money for breast cancer research.

I have found that when I haven't time to exercise, I miss it dearly.

I think none of us really believes we can be fitter in the future than we are now, especially once we reach our middle years. That is really not so surprising.

Ten years ago, I still had three children to support. Now, I am cash- and time-richer, plus I can reclaim the energies that I once poured into them.

The trick, I think, is to find the exercise that suits you - the one you won't dump when the reality of it kicks in and leaves you feeling more defeated and useless than ever.

I was prompted by my 50th birthday and the thought that for me, it was now or never. Except, as I discovered, that simply isn't true.

THE GUARDIAN