A survey of 140 people born in 1990 found that only 38 percent believed they had reached maturity on their 21st birthday.

London - Wearing tight jeans and a Uniqlo duffel, fuchsia pink ring-binder stuffed with notes about Existentialism under my arm, I stride into university, the typical undergraduate.

Changing classroom between seminars, I catch sight of a reflection in a swing glass door. Looking back at me, though, is not a fresh-faced young student, but an elderly woman. For a split second I wonder who that woman is. Someone coming up behind me perhaps?

But, of course, that undergraduate is me - albeit one who any day now will be entitled to free prescriptions on the NHS and cut-price tickets at my local cinema.

As the Queen gears up with incredible gusto for her Diamond Jubilee, I’m tentatively tiptoeing towards a 60th of my own.

Even if it were on the cards, I’m not sure I’d be up for bunting and fireworks on the Thames. But there’s no getting away from it: this Sunday, I turn 60.

It’s all very well for Cherie Lunghi, who is a fortnight ahead of me, to talk about “60 being the new 40” and to insist that rather than be slaves to vanity, we should “accept the inevitable”.

Certainly, as I age, I find the disparity between how I feel on the inside and how I look on the outside grows ever greater. Some days I feel 20; others 35; on a bad day, perhaps 50. But more than that? Never.

In class with my fellow undergraduates, I forget that I’m old enough to be the mother of most of them. Indeed, one of the lecturers is not much older than my son.

But right now, I can’t decide whether my upcoming birthday is a milestone or a millstone. It’s scary heading for senior citizenship in a society that places so much premium on being young, in which women of my age are invisible - unless, of course, they happen to be called Meryl Streep, Helen Mirren or Joan Collins.

It occurred to me the other day that the only way I’m ever going to get noticed again as I sashay along the pavement is if I inadvertently get my dress caught in my knickers. Or fall flat on my face.

Facing up to mortality is not something that concerns me. (We all have to do that at some point.) What I want to know is how to live life as a 60-something to the full, without behaving like a fool.

Should I be succumbing to ageing gracefully or is disgracefully the way to go? Or is there perhaps a middle way?

Unlike for our mothers’ generation, there’s no road map for being a woman of 60-plus today. It strikes me there’s a good, a bad and an ugly to this state of affairs. On the upside, far from slowing down, for many women fun and freedom beckon in their seventh decade, once your children have flown the nest.

While my parents at this age were planning their social life around bridge sessions and golf, my peers are booking online for rock concerts and wondering whether Glastonbury does concessions.

By the time they were in their 60s, my mom and dad had given up globetrotting and settled for a holiday apartment in Spain. Contrast that with the fact that several of my friends are organising adult gap years or busily spending the kids’ inheritance on exotic treks to visit the gorillas in Rwanda.

My friends still manage to find things to wear at Topshop or H&M, and, like Carole Middleton, swap clothes with their daughters.

Fashion may, for the most part, be aimed at the young, but there’s plenty of grown-up glamour to be found in upmarket labels such as MaxMara and mid-range labels from L.K. Bennett to Mary Portas.

Whinge as we might about hemlines being too short and a paucity of dresses with sleeves, there is no excuse for being a fashion frump, whatever your age.

And if, at 60, my mother was still gossiping with friends over coffee or, indeed, the fence, women of my age are doing it on Facebook, relishing the world of social networking.

I’ve discovered that I’m a far better student at 60 than I was at 18, when I dropped out of university. More focused, more confident, better able to analyse, question and contribute.

But that’s the good news. Now for the not so good...

By the time they reached 60, our fathers may have been thinking of retirement. No chance of that now for most men - or women.

We can’t afford to stop work. Personal pensions have been whittled away, the state retirement age has gone up, in many instances mortgages are still not paid off.

The majority of my women friends continue in some form of paid employment - and enjoy the engagement with the outside world this offers.

Others are busy doing the granny shift, helping their daughters and daughters-in-law with children who can be returned to sender at the end of the day.

I can’t see any harm in the fact that we oldies - yes, it’s time for a reality check if you still think of yourself as middle-aged - see ourselves salsa-ing into our 70s and beyond.

But when it comes to relationships, I’m struck by a truly worrying trend.

The only age group in which divorce is on the increase is among those of 60-plus (among all other groups, it has gone down).

For men in particular, it seems to me, when age comes knocking at the door, common sense flies out the window.

A couple of months back, a dear friend, married for 40 years since college, turned to his wife and announced he was emigrating to New Zealand to set up home with a woman he’d dated as a teenager.

He’d reconnected with her through Friends Reunited and, after secretly meeting up, decided to start afresh. At 65! His wife is devastated. His adult children are outraged.

The idea that divorce and starting over is the cure for the disease of old age is becoming increasingly common currency.

But this is denial of the worst kind. I thought wisdom was something to look forward to - not to sacrifice on the bonfire of our vanities.

While increasing numbers of 50 and 60-somethings are busy playing sex gods and sirens on the internet, many are discovering that finding a mate late in life is no easy task.

When friends’ marriages end in their 50s, the women discovered the joys of sex and dating anew. But now they’re in their 60s, they are facing up to the fact that they may have to spend the rest of their lives alone.

They’re getting on with life as best they can, but it’s not a prospect they relish. Some of those who were abandoned by their spouses are bitter; some who did the dumping are beginning to regret it; while those who have found new partners (me included) are counting their lucky stars.

In Western society, beauty has always been treated as a virtue, and with cosmetic surgery promising faces and bodies that deny the years, it’s easy to understand why women are increasingly desperate to turn back the clock.

There’s no refuting that women feel empowered when they view their surgically improved selves in the mirror - but 60 is 60, no matter what the smoke and mirrors say.

If I could rub a magic lamp, I might be inclined to lop off a few years. But then if I did, I wouldn’t have been born in the ideal decade for the modern woman to have been born in. Since the Fifties, women have enjoyed extraordinary advancement, and I feel privileged to have been witness and participant in them, rather than merely taking them for granted, as younger women today naturally do.

To be born in 1952, as I was, just as Queen Elizabeth II came to the throne, was to be born into an era of incredible hope following the horrors and privations of World War II.

Certainly Harold Macmillan’s pronouncement in 1957 that “most of our people have never had it so good” was true of my family.

My dad gave me a work ethic. At 18, I walked into my first full-time job on a magazine. I could type. I could make tea. And that’s all that was required to start on the long road to becoming Editor of Cosmopolitan. Today, you’d need at least a degree to get a week’s unpaid internship. And how lucky we were to be among the first generation to have the birth control Pill to save us from pregnancy.

And along came feminism to demand equal pay and to make sex discrimination illegal, to reclaim the night and stand up for battered women. We could marry young or stay single. Divorce without becoming outcasts or putting our family to shame. Have babies in our 20s or save them for later.

We could give birth with an epidural or deliver in a pool of water. Embark on a career, carry on working after marriage and get paid to have time off when we had our babies without fear of getting the sack. What a brilliantly exciting time to be young and female.

Of course, it wasn’t all plain sailing. Discrimination didn’t disappear overnight (it still hasn’t). Bosses still found ways to get rid of us if were pregnant.

But the options open to us - compared to those available to our mothers - were phenomenal.

That’s why I’m irritated when younger women complain about how difficult it is to maintain a work/life balance. No one said it was easy, and choice sometimes comes at a price.

There was a time when I paid that price with a massive breakdown and clinical depression that lasted two years.

I’ll never know for sure the cause, but I’m prepared to put it down to the stress of trying to be a good mother and a high-powered career woman coupled with a genetic propensity for depression on my mother’s side of the family.

But would I have changed my life if it would have guaranteed avoiding those two years of hell?

Full-time motherhood would probably have filled me with frustration, making me a worse mother in the process. Having a career but no child and missing out on motherhood would have been unthinkable. So no, I wouldn’t have changed a thing.

When I entered my 50s, I thought my life would become more mellow. I had no sense that my husband would leave me, I’d have two episodes of life-threatening surgery, would meet a new man at the age of 56 and find love again.

Nor did I know that having given up being a magazine editor, I would write three novels, become a newspaper columnist and return to university.

What might my 60s bring? I haven’t a clue, and I’d rather not know. But as with every other decade, there are bound to be losses as well as gains. To misquote Shakespeare, age will certainly wither me, but hopefully custom will not stale my infinite variety. Or my curiosity.

I’ve been to a number of big 60th birthday bashes lately, but I’ve decided to acknowledge my own in quieter fashion.

I have booked three hotel rooms for three days in San Sebastian, the gourmet capital of Spain. In tow will be some of the people I love most: my sister and brother-in law, my son and his girlfriend, and my partner. These days, nothing means more to me than friends and family.

Much cava will be drunk. Many courses will be eaten. Beaches will be walked along. And conversation, like the cava, will be in plentiful supply.

I’ll do my best to glam up for the occasion, and am hoping my partner will notice - as he usually does. But if no one else clocks me as I walk along the promenade, so what? Maybe being 60 means I’ve earned my invisibility.

Having spent so much of my life worrying about how I look and what others think of me, I’ve finally come to accept myself as I am, rather than need the constant reassurance that I’m an OK person.

To say I’m glad I’m not young any more would be a lie. But I’m not sad either. I remember the Swinging Sixties as if they were yesterday.

As I face up to the big 6-0, something tells me I still have a lot of living to do.

Time for the Swinging Sixties part two? - Daily Mail