Now for the latest in relationships: 'granny romance'. Hundreds and thousands of people in their sixties and older are plunging into online dating.
Why are sixtysomethings suddenly looking for romance - and sexual partners - at their age? Partly because there is more divorce in the older years than there used to be.
People are also living longer and they are no longer spending their old age saying their prayers. The baby-boom generation - those born in the 1940s - have always been demanding about what they want out of life and are now demanding more excitement in their sixties.
Thus there is the new genre in fiction: 'granny romance'. The novelist Hilary Boyd (aged 63) has emerged as the market leader, with her novel Thursdays in the Park which has sold 100,000 copies and has hit the No 1 spot with Amazon sales.
This novel is the perfect template of the granny romance. A grandmother, Jeanie, in a marriage that is beginning to wear thin, takes her little granddaughter to a local park each Thursday and there, by chance, she falls into conversation with a grandfather, Ray, who accompanies his small grandson there on a weekly basis.
Jeanie is about to turn 60 and she hates the way she is being consigned to the category of old-age pensioner. Her nice, but rather boring, husband wants them both to retire quietly to the country, although Jeanie is ready for no such step-change. Romance occurs, because Jeanie is ready for it. Perhaps also because there has been no sex in her marriage for the previous 10 years. The story takes off from there and, although it is pleasantly easy to read, there is a serious enough subtext: many women in their 60s don't want to be invisible; don't want to be written off.
Sixty is sometimes the juncture at which husbands and wives discover that they want different things from their remaining years.
As befits the age bracket, the sex scenes are tasteful and rather in contrast with another old-age romance written by Piers Paul Read - The Misogynist - which describes the excruciating embarrassment of timing the Viagra exactly to coincide with the planned bedroom scene.
Boyd, who takes her own grandchild to a local north London park regularly (although she swears that the story is not autobiographical), has touched a demographic nerve with her granny romance.
The book originally sold fewer than 1,000 copies, until it was launched as an online novel and then it suddenly took off, its reputation spread by word of mouth.
It's been translated into more than a dozen languages and Charles Dance is bidding for the film rights - to play the grandpa lover, Ray, who is, incidentally, in pretty good physical shape for his age.
What I thought was quite realistic is that striking up a conversation in a park while minding the grandchildren is a lot more sensible than trawling through the seniors' dating scene on the internet.
In the Boyd story, the characters embark on a conversation because they have something in common; they are able to explore common ground in a gradual and tentative way, without commitment.
I am not disparaging online dating completely - people have made happy matches that way - but it is a much more testing ambience for oldies.
With an online date, you are being asked to measure up to the requirements as spelled out; with a spontaneous encounter, if there's a chemistry, it will emerge.
Older people always have baggage from their past lives. There is a history, there are often grown-up children, there are past relationships. All that has to unfold organically and sensitively.
A literary genre has been born and there will surely be more granny romance. The sex has to be gentler and vaguer than in much adult fiction - the granny market is less inclined to the explicit.
There has to be a strong emphasis on the emotional relationship and on the interweaving of family networks.
Obviously, it's not every granny's cup of tea. Some women in their sixties have had quite enough of romance, thank you very much, and want to use their senior years exploring the road to Samarkand, or finally learning to play the violin, or even pottering around with gardening and golf with their well-worn, old spouses.
Some women even like being invisible, because it is a restful position from which to view the passing world.