I’m reluctant to write about older women in case it makes people think I’m one of them. After all, why would any woman wish to be associated with the post-menopausal hordes unless she had no choice in the matter? Anyhow, just so you know, I have not yet reached that point. I may be clinging on by my fingernails, but I haven’t yet crossed over to the dark side.

And what a dark side it is. While I don’t quite hope I die before I get old, I’m still desperately praying for an overthrow of the patriarchy before I get my first hot flush. Being an older women is, by all accounts, grim. It’s not just that women in their fifties are hit hardest by the gender pay gap, with most drives for pay parity aimed at their younger countertparts. Nor is it simply that, to quote a recent Guardian correspondent, older women “face daily insinuations in the media that we are ugly”. As women get old, their age is seen to cast a shadow over every contribution they make and every belief they hold.

As shown by the recent furore over Germaine Greer lecturing at Cardiff University, it’s not enough to disagree with an older woman. One must cast her as “a dinosaur” facing “a slow and painful extinction”. Thankfully, we do not have to witness too many of these pathetic creatures on our TV screens. While you can be a man in your 70s and still host mainstream current affairs programmes, the “woman of a certain age” tends to be shown the door (chivalrous as ever, the reporter Michael Buerk likens this process to “pruning the raspberries to make way for new growth”).

It’s a depressing state of affairs. Moreover, I do not think what we are witnessing is simply the intersection of ageism and sexism as separate axes of oppression. Rather, it seems to me that a particular form of ageism is integral to how sexism operates.

As soon as we go through puberty, women are told that the biological clock has started ticking. Regardless of whether or not we can or even want to have children, all of us have been given a sell-by date based around when menopause is assumed to start. It’s not that we then stop being useful; it’s that our usefulness becomes taboo.

According to the rules of patriarchy – a system which seeks both to appropriate the reproductive labour of women and to deny that a woman can do anything but gestate – a woman ought not to outlive her reproductive usefulness. Yet most women do, and for a very long time. What is more, they remain important to society, as workers, carers and thinkers. They hang around for another thirty-odd years, demonstrating that half the human race does not exist merely to be objectified and/or impregnated by the other half. No wonder so much effort has been made to devalue older women, these representatives of female potential whom one cannot even attempt to define solely in relation to men.

You would think, then, that younger feminists would champion the cause of older women. “Help the aged”, as Jarvis Cocker sang in a song only some people will remember, “’cos one day you’ll be older too”. To which, alas, the standard younger feminist response seems to be “no, I won’t. I’ll identify my way out of it.” Unfortunately older women have come to symbolise everything that contemporary feminism seeks to deny: biological necessity, the body, the limits of internal self-perception as the sole arbiter of truth. These women let themselves get old! How could they have been so stupid? Ageing is such a deeply unimaginative, essentialist thing to do!

Men are allowed to age. Their lives are not subject to the same schedule and cut-off point. Responding to the “male menopause” means buying a motorbike, getting a tattoo, perhaps taking up jogging. No one expects a man over fifty to disappear into oblivion. He still has something to offer. When young people draw on the work of older men, they do so to add stones to the edifice, or to stand on the shoulders of giants. When they refer to the work of older women, it is to show how out of date it is. Older men are still potent and virile. Older women are barren and intellectually spent. But don’t, whatever you do, draw any parallels between this and the rhythms of human reproduction. Patriarchy might genuinely operate on these terms, but only an ageing harpy would be ill-mannered enough to point it out. Only someone who no longer appears to be of childbearing age could be stupid enough to think that whether or not one appears to be of childbearing age has anything to do with the form of misogyny one experiences.

The tragedy of this is that all women eventually succumb. Not only that, but we’ve trained ourselves to see it as a failing on the part of the women who fell before us. In Of Women Born Adrienne Rich describes how “thousands of daughters see their mothers as having taught a compromise and self-hatred they are struggling to win free of […]. Easier by far to hate and reject a mother outright than to see beyond her to the forces acting upon her.” To distance oneself politically from the older woman is to assume that one will avoid her fate, at least until one becomes aware that a new generation of women are now distancing themselves from you. You discover, too late, that there is no way of ensuring that no one will notice you have body that is both female and getting older. Take whatever measures you like – from over-priced night creams to over-wrought self-definitions – but people will still know.

The denigration of older women cannot be a niche concern because, unless we are very unlucky, each of us will get old. Nor can we assume that we will be “better” old women, earning a place at the table unlike those bigoted old biddies who apparently deserve everything they get. Right now feminism and patriarchy seem to be in agreement about the point at which all women lose value. That leaves a very long time in which to be considered worthless. If we don’t speak up now, we shouldn’t be surprised if no one is listening when we most want to be heard.