“You’re not really 50 – you just look it.”

My friend’s idea of an amusing badge which she attached to my birthday card went down like a lead balloon.

The sad thing is, today I am 50 years old and I don’t want to be. Some women hate divulging their age, when asked, but I’ve never minded telling people how old I am – until today.

I don’t like writing it, and I’m going to hate saying it. I don’t want to know about ‘The Big 5-0.’ Thankfully, the 50-year-olds of today aren’t like they were when I was a child. Five decades ago, 50-year-olds wore girdles and sensible shoes, went on Beeline coach tours to Morecambe and expected people to stand up for them on the bus.

Now they are dressing younger, backpacking around the world and jogging into town.

Fifty is the new 25, the so-called Nifty Fifty, when the middle-aged have more fun than those many years younger. It is an age when 50-somethings are super-fit, and can out-run and jump those young enough to be their grandchildren. They are also having a better time socially.

A survey of 4,000 Britons aged between 18 and 75 found that a typical 50-year-old goes out twice a week, catches up with four friends and has three weekends away a year, but a 20-something has only one evening out, sees three friends and takes two short breaks. Half of all 50-year-olds say their focus is on enjoying life to the full, while only 30 per cent of 20-year olds say the same.

So why am I so depressed? Because that’s not how it is for me. I can’t afford to go out even once a week, holidays are limited to one week a year – self-catering in the UK, not scuba diving in the Maldives – and I rarely see friends.

Fifty should be an age when you are looking forward to retirement, but for my generation, with the cost of living rocketing, job uncertainty and pensions up the spout, it’s a case of work until you drop.

I’ll still be at my desk when I receive the Queen’s telegram.

Having started my family late, I’ve got two children who may want to go to university within the next five years. I’m already planning the bank job to fund this.

Fifty may be the new 25 if you’re absolutely loaded and can afford to spend every day in the gym or at the salon.

But for me, it feels like it’s downhill all the way. And if 50 really is the new 25, then why am I receiving catalogues full of shapeless skirts with elasticated waists and shoes with Velcro fastenings?