Is turning 50 the beginning of the end, or just the end of the beginning? The truth is that it's a bit of both. If 40 is the marker of middle-age (assuming one lives to 80) then it follows that 50 must be the gateway to old age: in other words, it's the time at which we have to face the terrifying truth that we have less time left than we have already had.

But perception is everything, and if we consider the unusually long list of high-profile personalities who reach their half-century this year, it seems fiftysomethings have never had it so good. Not for us, it seems, a slow and lonely descent into the twilight of life; most of us are still in the thick of it, working full-time, seeing off dependents on one or both sides of the generation gap, and enjoying active sex and social lives. According to Emma Soames, editor at large of Saga, the magazine dedicated to the over-50s, "It used to be that 50 was the new 40, but I now wonder if it's not the new 32 and a half."

Saga, the largest subscription magazine in the UK - current cover girl is Kim Cattrall, the 52-year-old Sex and the City star - has recently launched its own online forum aimed at creating a "community". Nothing, it seems, can shake the confidence of a generation that is now coming of age. "The late 1950s were a good vintage and a lot of very interesting people are now hitting their 50s," says Soames, who is 58. "They are mostly people in the creative and arts industries, and they are living proof that the baby boomers were always a bit different, and always had their own voice. We're the first generation to be as lucky at this age as we are."

Madonna turns 50 in August, and recently put it like this: "If I didn't feel good and wasn't doing what I wanted to do with my life, maybe it would bother me." The multi-millionaire performer, who will celebrate her birthday by embarking on an age-defying 50-date world tour, is unarguably lithe and fresh-faced but then, she is able to work out for at least three hours six days a week, practise yoga and follow a macrobiotic diet. "There are no shortcuts to being Madonna," she warned. "It's all about hard work. If you want to know how I look like I do, it's diet and exercise and constantly being careful."

The actress Michelle Pfeiffer agreed that eating well and "going at it hardcore in my gym" was the way to face the inevitable in April. And Jamie Lee Curtis, whose turn it is in November, has said: "I feel way better now than I did when I was 20. I'm stronger, I'm smarter in every way, I'm so much less crazy than I was then."

But is turning 50 really the happy-clappy experience it's being portrayed as by the sorority of celebrity seniors? Is it a case of the limelight ladies attesting too much? What is it really like for those who live ordinary lives and have to work full-time through the menopause?

"For me, turning 50 represented a giant step towards freedom and I celebrated with a party - something I didn't want to do when I was 40 and 30," says Margaret Timoney, a development worker with the Glasgow-based charity Outside the Box. "For the first time in my life I have nobody to look after but myself. It's very exciting. I feel I can do anything I want to do and that I still have a lot to give."

But in the months prior to her birthday last August, the divorced mother of two daughters, both in their 20s, admits she wasn't so sure. "I couldn't believe I was actually going to be 50. It seemed so old. I started taking stock of my life, questioning what I'd done with it. But as my birthday got closer I realised I had to go with the flow. Once it was over, I realised it wasn't so bad and that I'm not so different from what I was when I was in my 40s."

However, Margaret has started to dress a bit older. She still wears combat trousers and jeans at weekends, and pinstripe trousers with Birkenstocks for work. But no mini-skirts or smock tops.

"A lot of young fashion is really nice, but I feel I've been there and worn that. It would feel strange for me to wear smock stops and wedges, because that's what I wore in the 1970s, when I was in my 20s. Wearing them again would be like saying I'm trying to relive my past. At our age we need good quality. I think you can be more stylish at 50 by wearing classic clothes augmented by pieces from M&S or Gap."

The big issue for Margaret, who became a grandmother the same year she turned 50, is her health and weight maintenance. "I'm more aware of being less fit, and how hard it is to get fit. The fat just doesn't go away so easily," she says.

She was offered a 50+ check-up by her GP and had her blood pressure, cholesterol, height and weight monitored. She also had a mammogram, which in Scotland is offered to all women when they turn 50. However, she would not consider reverting to a gastric band, as the television presenter Fern Britton did when she approached the big five-0 last July, and as Anne Diamond did at 51.

"I haven't exercised for a long time, so I'm taking it slowly by walking as much as I can, swimming and doing a bit of yoga. It makes you sleep better and feel happier thanks to the release of endorphins. I'm enjoying it because I feel I'm doing something to help myself," says Margaret. "My big hurdle is entering a gym and facing all those younger, slimmer women, though."

She is grateful for health screening. "It makes you realise how important your health is and that you're in control of it. If you're going to have to be fit enough to work until 65 or 70 as most of us are, you have to look after yourself."

She points out that women who are divorced or working part-time need to ensure they have enough money of their own for their old age. "I worry about my pension. There are a lot of women in my position who worked part-time and have no or very little pension provision. It's a worry for all women, particularly if they've relied on their husband's income and pension. I'd encourage every young woman to get her own pension because you never know what will happen. When you're younger you don't think about these things. But like many other women of my age I have to keep working, both for my own financial security and for my own wellbeing."

And, of course, there's the M-word, which is rarely mentioned by ageing celebrities. Margaret feels lucky that her four-year menopause ended just as she turned 50. She tried HRT for two years because she wanted to avoid having hot flushes in front of clients and colleagues, until she realised it was "only putting off the inevitable" and came off it.

Emma Soames describes the 50s as entering a "new time of life", a window of opportunity that lasts until the mid-60s or early 70s before old age does set in. "A lot of people in their 50s change jobs or direction because they have that life is not a dress rehearsal' feeling, want to do something new before it's too late, and are healthy and wealthy enough to do it," she says.

Refreshingly, however, Margaret doesn't have the urge to change everything. She says she is content with her life and enjoys her job.

"If you see yourself as an old person you'll be one," she says. "I still have the rebellious streak I had when I was a teenager. But at least I'm enjoying my life. Unlike many celebrities I am not in denial about my age, I'm not having facelifts and tummy tucks, always going to bed early and only drinking water." It seems that today's army of fiftysomethings have decided that embracing early old age with artfully toned arms is much more rock'n'roll than desperately seeking regeneration.