When lines appear on your face and grey hairs sprout on your head, chances are you've got what it takes, says Pru Irvine
Did you know that middle age is a thing of the past? It's just for oldies now. According to Sue McGregor and Ann Leslie on Radio 4, diet, exercise and the "surgeon's knife" - oh, those words make me come over all funny - mean we can all look the same in our forties as we did in our thirties. And if we're really underfed and over exercised, we can even look the same as we did in our late twenties. Marvellous.

I was driving as I listened to Sue and Ann and the imprint of the steering wheel stayed in my hands for several hours afterwards. I squeezed that wheel and cursed. Excuse me, but I don't want to look like I looked in my thirties. I don't want collagen lips. I hate vegetable juice and I consider all forms of physical exercise to be a sign of mental anguish.

In fact, all my adult life I've wanted to be 40. At 16 I thought being 40 would free me from the anguish of making friends. By the time I'd reached my early twenties I thought 40 would be the age to say exactly what I wanted without being dismissed. And as that decade slipped into the next I found myself up to my neck in job, marriage and children. I looked towards my forties as the period of having come through. It promised to be the era of the re-invented me; my friendships would be harnessed and I would be less anxious about my views. I would also be old enough to be taken seriously.

Well, it's all going to happen in the next couple of weeks and no one, not even Dr Mac The Knife is going to persuade me this is not a good thing. Next to being psychoanalysed, sterilised and meeting my husband, being 40 is going to be fourth best thing that's ever happened to me.

When I was just a girl, in my thirties, I had a rather serious and high- flying career. I was in my Paul Costelloe and white BMW phase. The world was my oyster, provided I kept my buttocks clenched and my nails painted. But there were problems. I was so young I could smell burn-out at 35. I also had no sense of future: in those days the future was about your ability to push up your salary at the annual review. Now, in the second half of my life, I have a past that I know about. I like having a past. It makes me feel important.

How's this for a headline, courtesy of the Scotsman newspaper? "The female eccentric - the only glamour job left to the over-forty gal". The writer whinged on about insurance policies displacing black knickers and the need for a Superwoman role model when you hit that "confidence-sapping juncture" of 40. I think she mentioned Margaret Rutherford. Well, honestly. Let's get this into perspective. The lines on my face show that I've lived. My greying hair says I don't feel the need to dye it and my podgy little arms say I've got better things to do with my time than pump iron. My knees were always fat.

According to July's Tatler magazine, middle age is now leather trousers, short skirts and fabulously blonde hair. I think what this facile description means is that anything other than a tit on a stick is just so un-cool that you might as well look like the Queen. I mean just look at the Queen, says Tatler, she's been middle-aged for a million years. Really? Well that's just the point, isn't it? Some people are born middle-aged and some, like me, aspire to it. Can you see the Queen in a fabulously short leather skirt? I've never been exactly a paisley girl myself but my wardrobe has been the same since I was allowed to choose my own clothes. Sometimes I've branched into navy and sometimes into silk. But not often.

Now this brings me to the crux of the matter. HRH may have been born middle-aged but that doesn't tell us anything about her sexual prowess. Who knows what beats inside those endless matching hats and bags. The truth is girls, you can't beat 25 years of experience in bed - or in the car (unless you're fifty, of course). Hands-on anything for that length of time is bound to make you an expert. But I'm afraid you have to be forty to know that. And this is what we're talking about, isn't it - being able to do a good job welln