"How old are you? How old do you look? How old do you feel? How old do you wish you were? Or looked? Or felt? Bruce Forsyth, 85, said this week that he feels 30 on stage. Joan Bakewell commented that as she turns 80 she finds the notion that her time is running out inescapable.

Most readers, I think, will find it similarly hard to give uniform answers to the questions above. My own vary by about 10 years. I’m not giving you exact numbers on the grounds that they might incriminate me.

The range of answers the average person – and, for reasons we’ll come to, especially the average woman – will give in response surely requires that we have some sympathy for Junie Hoang. An actress, Hoang recently sued the website IMDb (albeit unsuccessfully) for publishing her real age instead of the seven years younger one that she had provided, resulting – she said – in loss of work.

Actors and actresses have of course always lied about their ages – especially in the days before the internet could immediately find you out. Search for any of the stars who twinkled in the glory days of MGM’s studio and their birthdates will usually include a question mark or two. These days, there exists a ‘PR age’, because the practice of knocking off a few years is so rife in the industry. We had a family friend – long since gone to her reward, alas – whose husband never knew her real age, but it was at least 10 years older than he thought.

Age is a funny thing. On the one hand, it means less than ever before. You can shop in Topshop from 14 to 40 (though you might have to exercise a leeetle care at the upper end of the scale). You can go clubbing whether you have to sneak out of the house to avoid waking your parents or your baby. You can enjoy Glee whether you long to be Rachel or Quinn when you grow up or whether you could technically be the mother of any one of the cast and probably crew. When our parents were young, 50 was old, 60 was dangerous and 70 was the point of collapse into decrepitude, disease and death. My parents are 70-plus and they’re both fitter than I am. We’ve extended our fertility, our lives, our horizons and lost track of where the old markers of ageing were and where the new ones should go.

On the other hand, our culture is ever more youth-obsessed and the pressure to remain fresh of face, dewy of eye, pink of liver and uncankered of soul increases inexorably.

When youth is overvalued, we all have motive to lie about our age and, if you work in a field in which it is fetishised as well, naturally you are more vulnerable. Equally, when the definitions of different ages are confused, the desire to blur the lines strengthens.

Our collective mental image of what 30, 40, 50 looks like lags far behind the facts. When I see “38-year-old mother of two” written anywhere, I still conjure up a picture of a woman in sensible shoes and an elasticated M&S skirt, despite the fact that most of my closest friends could fit this description and are absolutely unrecognisable as anything to do with this stock picture. Similarly, if I read about a 70-year-old grandmother, I don’t think of my mother – tall, slim, looking better in a swimming costume than I do and running gleefully all over creation with my toddler son – I think of a bowed little woman with a grey perm, slippers and a faint smell of ammonia hanging apologetically in the air. My mother looks and acts like the person I imagine if I think of a generic 50 year old, and if it didn’t throw the maths off and require me to pass for 18, I would describe her to others as that. And why not? Our opinions and treatment of people can change so drastically depending on whether the numbers skew a tiny bit one way or a tiny bit the other that a small lie can seem, in a twisted way, to provide a greater truth.

But of course it’s because we still carry these prejudices and therefore frequently prefer to obscure our real ages with a lie – that better represents the way we feel we are inside – that the stereotypes remain. I would do my bit for the greater good now and nail my own chronological colours to the mast, but alas, I have to go. I have some navy blue court shoes and an elasticated skirt to buy.”

Email Lucy at lucy.mangan@stylist. co.uk or tweet her @LucyMangan

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Additional image credit: Rex