Who is having the most sex is a 21st-century preoccupation. There’s nothing we don’t want to know about the sexual habits of healthy adults, by which we mean people under 50. It’s not that we are ageist; we just don’t see the point of including a group who are past it (the UK National Survey on Sexual Attitudes only bothered to talk to people under 44 – that’s three years younger than Nigella, but never mind). Which is why a new study by the American National Institute on Ageing has come as a shock. To summarise, 65% of those aged 65 to 74 reported having sex at least twice a month, and three-quarters of 57-to 64-year-olds described their sex lives as “active”.

That’s right: sex does not end at 44, and many claim it only gets better. But then, we don’t need a survey to remind us how narrow our view of sexuality is. Here’s a rough guide to our actual experience of sex, decade by decade (look away now, UK national survey man).

Twenties to thirties You are self-conscious to the point of combustion; he is self-obsessed. This means you are freaked out about how you are doing (too needy? Too wobbly?), while he thinks he is being judged on aerobic impact and hits per session. Your boyfriend appears to be great at sex, but later you discover that he was miles off course and you mistook a mat workout for the real thing. 4/10

Thirties to forties This is the decade of performance pressure (should you have some tricks by now? Furry handcuffs?), plus you are too distracted to focus because you are subconsciously stressing about whether this is The One. (You don’t recognise this until The One comes along, after which you feel able to admit that doing the bendy thing gives you indigestion. This is progress.) Then you have children and start juggling, and you are knackered, which brings about a whole new level of performance anxiety: you must do it, even when blacking out through exhaustion, for the sake of the relationship. Grrr. Meanwhile, he is thinking about work and worrying that his sexual prime is being spent with someone who actually says: “Okay, then, but be quick.” 7/10

Forties and fifties Bye-bye, inhibitions. Finally, you are over the selfless years and very keen that you have satisfaction regardless. Plus, you are more sorted on the domestic front and fancy yourself more because, at last, you can afford a decent haircut and gym membership. Meanwhile, he has worked his way up the tree and has arrived in the “patient study” zone. By now, he has twigged that plenty of unselfish sex is a better means of controlling your mood than Valium. You are thinking: “More!” He is thinking: “Maybe that will make her less grumpy.” 9/10

Fifties to sixties Bull’s-eye! You are home alone and, according to Guy Ritchie’s stepmother, Shireen, in the Daily Mail, lighting candles and dancing around in a romantic fug. Who knows? (Shireen gives it a 10.)

Sixties to seventies Yuk. Can’t go there. Give me another five years.

Times recommends

• Ingrid Betancourt's homecoming
• Geraint Anderson: Trust me, greed ain’t good
• The 10 best campsites in Greece