There are certain commonplace events that rarely make it into screenplays. Characters in films don't drive in circles looking for a parking space, nip to the corner shop for loo roll or – with the dishonourable exception of Woody Allen – have sex if they're over 50.
While parking is a viable, if boring, topic for real-life small talk, according to Age UK, the sexuality of older people is as unmentionable off-screen as it is on. "Our research has shown that while advertisers and the media promote sexualised representations of younger people, sex and older age is widely viewed as a taboo subject," says Michelle Mitchell, the charity's director general. "We found that many people are often reluctant to even acknowledge that sexuality in older age exists."
Or so it was. This week on general release is at cinemas is Hope Springs, a mainstream comedy-drama starring Oscar winners Meryl Streep (a ravishing 63) and Tommy Lee Jones (a youthful 66) as a couple who go on a week-long sex therapy retreat in hopes of restoring intimacy to their 31-year marriage. They discuss foreplay, threesomes with a neighbour and attempt fellatio in the back row of the cinema. In other words, it's absolutely filthy. But it's also an intelligent, brave and genuinely moving account of a grown-up sexual relationship.
So how did an anti-ageist cultural revolution get started in Hollywood, the Cult of Youth's holiest city? Simple box-office economics, says Joel Hopkins, writer-director of the 2007 romantic comedy Last Chance Harvey, "All this buzz feels completely obvious to me. My parents go to the cinema probably once a week. They go way more than I do. I've got small kids." Hopkins is now in post-production on The Love Punch, a romantic caper starring Emma Thompson (sprightly at 53) and Pierce Brosnan (a distinguished 59) as a divorced couple who team up to steal back their pension fund. It's a "fun and sexy" film, he says, but not over the top. "I don't know if this is true, but I think that older audiences are a bit more aware of when sex is gratuitous, when it's not integral to the story, but if it is, then they're fine with it."
From the dawn of the blockbuster era, the most bankable movie-going demographic has been about 40 years younger than Hopkins' target audience. The 18-24 year-old Slightly Nerdy Young Male queued round the block for Star Wars in the 1970s, quoted Top Gun in the 1980s, and collected Lord of The Rings memorabilia in the early 2000s. By 2010, however, he'd started downloading films straight to his laptop. An ageing population stepped in to fill empty cinema seats and Hollywood has been unashamedly courting "the grey pound" ever since.
British filmmakers have proved particularly successful at delivering mature cinema for mature moviegoers. The King's Speech is often cited as an example of the grey pound in action and last year's The Best Exotic Marigold Hotel, about the romantic escapes in an ex-pat retirement opened with an impressive £2.2m at the UK box office.
Yet while mainstream rom coms, such as Nancy Meyer's Something's Gotta Give (2003) and It's Complicated (2009) have successfully cashed in on the underserved over-50s audience, sex in these films is usually either the butt of a joke or depicted in patronisingly cosy terms. Unblushing realism has remained the preserve of boundary-pushing arthouse fare such as Germany's 2008 film Cloud 9. "Up to now we've had a link between youth and sexuality," says Susan Quilliam, consumer correspondent at The Journal of Family Planning and author of the updated 2008 edition of The Joy of Sex. "You get the image that only celebrities under the age of 30 are swinging from the chandeliers and the rest of us are drinking our cocoa and going to bed."
The guardians of our sexual health would beg to differ with that stereotype. Rising divorce rates and longer lives have led to a statistical spike in baby boomers, old enough to know better when it comes to safe sex. Between 2000 and 2009, 45-64 year-olds saw the biggest rise in biggest rise in syphilis, herpes, chlamydia and genital warts of any age group. They also saw the second-biggest rise in gonorrhoea cases, beaten only by the over 65s.
Part of the reason for this rise, says Quilliam, is the media's reluctance to acknowledge the existence of sex after 50. "The depictions of sexuality with older people are usually within the context of committed relationships and although I'm not suggesting that they whip out a condom on screen at every opportunity, if it were brought into the open in a sensible, well-scripted conversation, it would help a lot."
Industry assumptions about what mature audiences want to see are now changing says Jamie Schwartz, senior vice president of marketing at Momentum Pictures. "Older audiences aren't prudish about sex in films at all. The 'no sex please, we're British' attitude is a thing of the past." Momentum are the distribution company behind Hope Springs, Last Chance Harvey and Quartet, Dustin Hoffman's first directorial effort for more than 30 years, about a home for retired opera singers. "When we spoke to people who'd seen [Hope Springs], they loved the cheekiness and humour," says Schwartz. "'The saucier the better' as someone said in a research group."
If anyone is blushing at the prospect of Lady Thatcher and Men In Black's Agent K enjoying a passionate snog, then, it's not the over 50s, but Slightly Nerdy Young Male again. Fortunately for fans of nuanced drama, the film industry is no longer very interested in what he thinks.
So will movies such as Hope Springs herald the dawn of a new age of sexual permissiveness? Like a true Hollywood realist, Hope Springs director David Frankel is only very cautiously optimistic. "Probably not. Nobody ever really wants to think of older people having sex, even older people. But we'll all be older people one day and we'll all still want to have sex, won't we? So it's nice to see a movie that offers a glimpse of that possibility."