Contrary to popular belief, middle-aged and older people enjoy sex, and will do so into their 80s, research suggests.
The study found the more equal couples were the better the sex
A study of 27,000 people aged 40 to 80 in 29 countries also found couples with greater equality in western Europe were more likely to enjoy their sex lives.
Highest satisfaction levels were reported in Austria and Spain and the lowest in the more male-dominated societies of the Middle East and Asia.
The study is due to appear in journal the Archives of Sexual Behaviour.
Study author and professor of sociology at the University of Chicago Professor Edward Laumann said people aged 40 to 80 actually "engaged in a significant amount of sex".
He suggested this may well be a surprise to their children.
Bristol-based urologist Clive Gingell, who worked on the study, told the Guardian: "The majority of men and women are having an active sexual life past the age of 40 and up to their 80s.
"It's surprisingly high in all countries, with between 70% and 80% of people saying they have had sex in the previous 12 months."
The researchers looked at the experiences of men and women in countries including China, Japan, Indonesia, Thailand, South Africa, Turkey, Egypt, Morocco, Israel, the United States and most of western Europe.
But the research, which analysed the results of questionnaires carried out by urologists, psychologists, epidemiologists and sexologists, also revealed significantly different rates of satisfaction between men and women.
In every country, except Algeria and Malaysia, men were more likely to report they were happy with their sex lives.
Professor Laumann said: "Women are very sensitive to the quality of a relationship and when those things aren't in good order they're not interested.
"It's a way of regulating (pregnancy) and protecting the children."
The lack of foreplay was also a reason for lower levels of satisfaction between men and women, the research suggested.
This was particularly problematic in some male-dominated cultures in Asia and the Middle East, Professor Laumann said.
Men needed a shorter time to reach a sexual climax than women, this was why foreplay was so important, he added.
"In 75% of the cases the men report always having an orgasm. With women only 26% say they always have one, although 45% of men believe their partners always have an orgasm."
However, where the two sexes experienced greater equality - essentially in western countries - 60 to 80% of subjects said they had good sex.
Couples in Austria topped the good sex league with 80% of men and 63% of women saying they were enjoying extremely or very satisfying sex.
In second place came Spain, where 73% of men and 68% of women reported high satisfaction rates, the study suggested.
But in "male-centred sexual regimes" like the Middle East, Brazil, Italy and parts of Asia the study suggested satisfaction rates fell to the 40-50% range.
Languishing at the bottom of the league was Japan, with just 18% of men and one in 10 women telling researchers they had good sex.
Liz Hadland, a psychosexual therapist and spokeswoman for the British Association for Sex and Relationship Therapy, said it was interesting that there was a realisation that older people do enjoy a sex life.
She said younger people may feel less satisfied because they were often under a great deal of pressure from magazines, films and the media to achieve a perfect sexual experiences.
"There's so much hype about multiple orgasms and how many times a week people have sex and young people can be very body conscious."
She also suggested women in more male-dominated countries may not have ownership of their own sexuality in the same way that women in western countries do.