Older people are living longer and in better health than ever – so of course they're continuing to have sex. Why is it so hard to talk about, asks the editor of Gransnet

Ten years ago in New York, I interviewed Helen Gurley-Brown, the kittenish but formidable creator of Cosmopolitan, who was then 80. Without preamble, she launched into enthusiastic endorsement of a lubricant called Astroglide: "You be sure," she said severely, "that you're all goopy before you get into bed." At the time, I was taken aback. Now I am older, it seems less funny.

Young people are often surprised that older women have sex at all. On Gransnet, the social networking site for grandparents that I edit, one poster described celebrating her 55th birthday at work and being asked by a much younger colleague at what age she had given up sex. She replied that she'd let her know when it happened; the other woman, she said, "looked horrified".

In fact, people over 60 are now the fastest-growing group contracting sexually transmitted diseases, according to government agency figures. Since 2002, syphilis has tripled in the over-65s in the UK, and HIV is up by 60%. Even allowing for the fact that we're starting from a low base, this is clearly not post-menopausal purdah.

Much of the ignorance about sex and the older person stems from resistance to thinking about old people at all, least of all their yucky bodies. There is a profound cultural fear of ageing, which glorifies the young and deprecates anything old: "ageing infrastructure", "sunset industries". This distaste tends to feed a perception of older people as a homogeneous group – which is absurd, because we tend to become more diverse, more assertive about our likes and dislikes, as we age. This is likely to be as true of sex as of anything else. Certainly, the impression that discussions on Gransnet give is that there's a spectrum of activity, from "none and not bothered" to "lots and up for more". Some of it may also be highly inventive, if only out of necessity.

When one Gransnetter asked recently: "If 16 is considered too young for sex, when is too old?" the majority view was summed up as, "when you can't remember what sex is", and "I'll tell you when I get there". There's clearly one big plus to being older, in that intimacy benefits from time and a lack of toddlers and teenagers. "Thank God for HRT and retirement – it's better than ever (aged 58)" says one poster. "I don't care who's programmed to do what or when," says another. "I've been married for nearly 40 years and have no intention of giving up our siestas and weekend lie-ins."

As the HRT reference suggests though, menopause can trigger a crisis. Those who sail on through it may well have to adjust, to make use of Astroglide-type aids or other chemical assistance. But among those who do slow down, it isn't necessarily (or mainly, according to our admittedly self-selecting panel) women who make the decision. "My husband has never tried to have sex since a 'failure' (the first ever) 16 years ago – since then it has never been discussed."

"We haven't bothered since 1999," says another woman. "There was no discussion or decision, it's just never been mentioned since then – on a holiday to Tunisia, to be precise." A combination of reticence and a bland assumption by young GPs that menopause will put paid to sexual desire leaves some people accepting that sex doesn't go on for ever, though not all are reconciled to the idea. Some are left with a sense of mourning: "I miss wanting sex as much as the sex itself."

Menopause may not, of course, be the only or main cause of waning desire, even when it takes the blame. New relationships have a suspicious habit of reviving enthusiasm. "It's much better when you live alone and have 'visits'," says nanachrissy. "When I was married, I think sex was spoiled by underlying resentments and suppressed anger. Now there are no strings and sex is the best ever. Also I have no hangups about my body, because I don't really care what he thinks (although he is very kind!)."

The memoirist Diana Athill writes, in Somewhere Towards the End, of her sadness that making love with her "dear habitual companion" had staled: "Familiarity had made the touch of his hand feel so much like the touch of my own hand that it no longer conveyed a thrill." She assumed this was a question of her age – she was in her late 50s – until she met someone else and experienced what she thinks of as a reprieve: "I found, to my amusement and pleasure, that novelty could restore sex."

Nora Ephron, who has written entertainingly about ageing, maintains that if you're lucky enough to be having sex in your 60s, you won't be having the sex you had in your 20s. This is probably true, although it doesn't have to be worse. Some Gransnetters claim to be having the best time of their lives. The ingenuity of people with dodgy hips should not be underestimated, nor, for those with less than fighter-pilot reactions, should Slow Love.

When Jane Juska was 66 and living in Berkeley, California, she placed an ad in the New York Review of Books: "Before I turn 67, next March," she wrote, "I would like to have a lot of sex with a man I like. If you want to talk first, Trollope works fine."

Her bestseller, A Round-Heeled Woman (and the play adapted from the book, starring Sharon Gless, which finishes a West End run this week) catalogues a sexual odyssey that is by turns alarming, sad, funny and pleasurable.

Menopause, according to Gloria Steinem, can give women a new drive and confidence. "What we lose in those menopausal years is everything we needed to support another person," she argues. "What we keep is everything we need to support ourselves." Former Columbia Journalism Review editor Suzanne Braun Levine takes this as her cue in a new book, How We Love Now, arguing that older women have more satisfying experiences of intimacy because we can shuck off expectations of femininity, niceness and acceptability, to be more honest about desire.

Internet dating sites have made finding someone to suit this new, more assertive state easier. There are some that are specifically (and by some accounts successfully) targeted at people in the second half of life, though one Gransnetter warns, to no one's great surprise: "All the old men of 70 think they are only 40, so that's the age of woman they are looking for."

Sex, for most people, does tail off at some point, though there's little consensus about the timing or rate of decline. For some, it may stop abruptly on an otherwise unremarkable holiday; others have every intention of continuing to the end of their days and will point out that less frequent doesn't always mean less intense.

Greater longevity and improved health mean that a phase of life never previously seen now exists: an extended middle-age: fit, competent and interested in sex. The novelty of this means that very little is understood about its erotic possibilities – but these are likely to be as varied as for any other group and, probably, more so. "Don't give up hope," one woman posted recently. "I speak as one who met the love of my life (and he really is just that) six years ago after 15 years of (intentional) celibacy. I'm nearly 74 and he's 56." Meanwhile, another poster reported that she knows of one 80-year-old care-home resident who insists on having her vibrator passed to her every night.

gransnet.com