On a zipwire into my sixties Jim White

There was a moment, as I was hanging over the lip of an abandoned slate quarry in Snowdonia, when I wondered what on earth I was doing.

Why had I allowed myself to be attached to the fastest zip line in the world and the longest in Europe, a device that dispatches visitors at more than 100mph down a vertiginous slope while they lie suspended more than 75 feet above razor-sharp scree?

There comes a time in a person's life when they are surely too old for this sort of nonsense, too wise to be feeling their lunch rapidly making its way up the throat fuelled by a surfeit of undiluted terror. And, if turning 60 doesn't give a hint you have passed that point, then nothing will.

A friend thought it an ideal 60th-birthday present. Never mind treating me to a cream tea at the Savoy, a night at the opera or a bottle of something tidy. Instead, I was fired along a thrill ride known as Velocity 2, in a place called Zip World in Penrhyn quarry, just outside the former mining town of Bethesda, north Wales.

And the odd thing was, on a glorious autumn afternoon, I wasn't alone as a thrill-seeking oldie. Everywhere I looked, at appropriate social distance, there were bald heads, grey hair and middle-aged spread. In the off-peak time, when the school summer holiday trade has dissipated, it seems the majority of those turning up to Zip World are similarly marking their transition into advanced age. After my ride, I met a chap who was there to celebrate his 80th.

‘ Fantastic,' he said. ‘ Made me feel young again.'

Which is the point. What we were all doing on our Welsh adrenalin rush was proving we were still not past it.

And Zip World is clearly doing very well out of the grey pound, cleverly monetising our collective need to cling on to wild youth. Dame Judi Dench had a go on it recently. Her picture, showing her grinning wide in the excited aftermath of her ride, is there on the wall, one of many silver-surfing Canutes seeking to hold back the tide of time.

Despite the suggestion of mortal danger, the fact is that this is a safer exercise than heading down the stairs to the wine cellar. Nor does it require any particular skill. Unlike other adrenalin activities, the most strenuous physical input is a gentle walk up to the initial launch point.

Yet, when it begins, after weights have been applied to your back to ensure you aren't buffeted by the wind, the safety crew have supplied a rocket-launch countdown, and you are pinged off down the wire, it is a magnificent sensation.

As you swish over the extraordinary scenery, travelling so fast you can't hear yourself scream (and boy, I tried), the fun is jaw-dropping. Arriving all too soon at the finish station, being unclipped and lowered back down to earth, you find yourself skittish with adrenalin.

That is when it becomes properly clear why you have done it. That is when you feel an emotional uplift that allows you to forget what birthday it is you are marking. Well, almost.