A few months ago I interviewed Warren Beatty and told him that it was crazy for him to pick 26-year-old Halle Berry as his love interest in Bulworth when he was old enough to be her grandfather. He listened politely, and nodded, and said he took my point. But then we wandered down to the lobby of the Dorchester Hotel where two 16-year-olds, in low cut tops and lots of lip gloss, were waiting to talk to him "for a school project".
He stopped and had a few words with them, but while he was just polite they were giggly and enthusiastic, and clearly desperate to extend the interview. How can you tell such men that they can't put themselves up as lovers of 20-year-olds when they live in a world where teenagers are throwing themselves at them?
How can you tell the old and ugly Woody Allen that no one will buy him going to bed with a young and lovely Julia Roberts in Everybody Says I Love You, when in real life his young and lovely wife Soon-Yi is so eager to oblige?
So, even as they age, film stars feel confident about casting themselves as great lovers. They live in a warped world where a halo of past sexiness, a whisper of power, a frisson of Hollywood glamour, is enough to make girls who would never look twice at them if they were cabdrivers or bricklayers jump into bed with them.
But who isn't sick to the stomach at the way they play that power? To see all these fresh-faced female actresses, desperate for success, having to pay for their chance of fame by pressing their beautiful, smooth bodies against those of these raddled actors makes you feel like running from the cinema.
And they're all doing it, with not just Warren Beatty and Woody Allen, but Clint Eastwood jumping 45 years in his latest film, True Crime, to plant a kiss on the lips of a smiling 23-year-old; Michael Douglas jumping 29 years to get Gwyneth Paltrow in A Perfect Murder; Jack Nicholson 26 years for Helen Hunt in As Good as it Gets; Robert Redford 24 years for Kristin Scott-Thomas in The Horse Whisperer; and coming to our screens soon, Sean Connery leaping a 40-year age gap to embrace Catherine Zeta Jones in Entrapment.
Will this ever change? Or will we go on and on and on living in a world where the same frame is constantly repeated, where every second movie we go to ends in a clinch between a golden goddess and a wrinkled has- been? And, much more to the point, will we ever escape that scene in real life, or will we be constantly hearing about a 52-year-old president having oral sex with a 25-year-old intern; a 63-year-old film director living with a 28-year-old college student; a 73-year-old porn magnate clubbing with six twenty-something models; our chief inspector of schools being accused of a relationship with a teenage pupil?
The evolutionary psychologists, those scientific apologists for the status quo, are sure that this scenario will never change, that it was laid down in our evolved heritage for women actually to find older men sexier, and for men to go for the kids. A study carried out in 37 countries by the American psychologist David Buss showed that: "Men in general desired younger partners... Women desired men who were older than they were."
And Buss backed up that survey with the usual Darwinian explanation, the one that makes most of us feel we're not hearing an argument, but entering a prison - that this is the way it must be because this is the way it has always been. Once upon a time, men only wanted fertility from their partners, so they went for the one of the youngest girls in the tribe. However, women needed resources from their partners, so they went for the guy who'd had time to stash away a few bucks in whatever the Pleistocene equivalent of Wall Street was. And that behaviour was laid down in our genes and now we just can't get rid of it.
The whole scenario sounds pretty fishy - a typical case of an older male scientist seeing something that he set out to discover. If women had wanted resources from their mates in that mythical hunter-gatherer environment, you could argue that they must have evolved to go for gleaming young men with defined muscles and bright eyes, good evidence of keen hunting strategies. And if Buss had managed to find one country, out of all his 37, where women have equal access to status and resources, he might have found rather different mating strategies.
Happily, whatever explanation they try to put up, we can tell that the Darwinists are wrong because things are beginning to change. That change might look slow to us, but if you put it on an evolutionary timescale it probably appears dizzyingly swift.
Although Hollywood has been dominated by scenes of the older man and the ingenue for decades - with, always, the odd honourable exception - now, producers and directors are waking up to the fact that in the love stories audiences really want to see - the ones that do great box-office, win Oscars, and spark the fantasies of millions of young men and women - the tale revolves around exactly the opposite scenario.
They centre on a woman throwing over a powerful man for a younger, prettier and less controlling lover. Take Titanic as an example. Or Four Weddings and a Funeral. Or Shakespeare in Love.
And maybe the old boys of the screen are beginning to see how silly they look. Indeed, in the last film out that showed the usual clinch across the generations, True Crime, Eastwood injects some self-knowledge into the scenario. So in the very first scene, when he plants a kiss on the lips of a 23-year-old babe, she makes such a quick getaway she crashes her car; and in the very last scene, when he tries chatting up another young girl in a shop, she just smiles dismissively and sends him on his way.
And although women have kept away for so long from choosing younger lovers themselves, there are signs that, as they become a little more powerful and confident, that is beginning to change. The change is visible not so much in the cinema, interestingly, as in that strange place called real life.
Hollywood is looking much more traditional than it need be. Take just three stories that were all reported in the papers last week. One, the announcement of the pregnancy of the actress Caroline Quentin, whose partner is 10 years younger than herself; two, that Della Bovey, whose husband moved out to live with Anthea Turner, is in a relationship with a "dreadlocked labourer 11 years her junior"; and three, the case of a 43-year-old matron at a public school in Oxfordshire who's had a wild sexual affair with a pupil of 17. "Sometimes he skipped so many lessons we made love five times a day," she told the tabloids.
These women aren't, as yet, stretching to the 30- and 40-year age gaps beloved of the wizened old male movie stars, but their behaviour shows the rumblings of change in the way women want to live their sexual lives. And one day, perhaps, Hollywood will wake up to that. In 20 years time, maybe it will be Sharon Stone and Madonna who are taking on the kids.