Why is one dog year equal to seven human years – at least as far as film casting agents and male directors are concerned? HADLEY FREEMANon why women apparently speed-age after 30

IT MUST BE down to the Californian water, but something seems to happen to the women in LA so that they speed through the years at a far swifter rate than that of their male contemporaries. According to film casting agents, anyway.

It is all too easy for a female actor to find herself cast as the mother of someone who once played her boyfriend as soon as she blows out the candles on her 35th birthday cake. This has long been an accepted fact of Hollywood life, and one that most women keep schtum about as they know they should be grateful to get any roles at all in their decrepit post-30s.

But recently, Hope Davis finally broke ranks to admit she was somewhat “peeved” when she was recently offered a role playing the mother of Johnny Depp, a concept that would have tested the skills of the most talented special effects department, seeing as Davis was actually born the year after Depp.

Of course, nothing new. Hollywood has been moving that way for a while. Mel Gibson apparently believes that girls are awfully precocious in Denmark as he cast Glenn Close as Gertrude, his mother, in his 1990 film version of Hamlet, meaning that she would have to have given birth when she was nine. Isn't it nice to see a man so comfortable with his own self-delusions?

Angelina Jolie seemed to take being cast as Colin Farrell's mother in Alexanderwith good grace, despite being only a year older than him. But then again, maybe she was too busy considering whether she should adopt him to bother to take offence. Then there's Forrest Gump, in which Sally Field plays Tom Hanks's mother: not only is Field only a decade older than Hanks, but only six years before she was playing opposite him as his romantic interest in the movie Punchline. Lea Thompson was exactly the same age as Michael J Fox – 24 – when she played his mother in Back to the Future, while Elizabeth Taylor was a mere four years older than Dennis Hopper when she played his mother in Giant.

Quite why film directors are so averse to having middle-aged roles played by middle-aged women comes down to male insecurity and misogyny. In regards to the former, if the mother is played by, say, a thirtysomething, that would suggest that the male lead must be still a teenager. Yes, yes, Mel, the years may have passed for Glenn Close but you’re still a lithe, hot young thing.

As for the more obvious issue of misogyny, the sense of disgust of older women is so deeply entrenched in Hollywood that even when the role is specifically for an older woman, no one wants to see an actual older woman on screen. Far better to haul in Angelina and sod the obvious discrepancies.

Film audiences have long become inured to elderly actors being paired off with barely post-pubescent females. So those who are roughly the same age as their male counterparts are seen as, by extension, fair game for being cast a generation older.

As funny chance would have it, the actors who commonly play opposite much younger female actors often carry this habit over into real life, usually taking the age gap even further than casting agents would dare. That icon of wannabe silver foxes everywhere, Jack Nicholson, has a 16.7 year gap on average between him and his leading lady, while one of his longer relationships offscreen was with Lara Flynn Boyle, 33 years his junior.

Let’s not even get started on Woody Allen, another fan of romantic age gap discrepancies in his films, and his real-life move from the mother (Mia Farrow) to the daughter (Soon-Yi Previn). The question of whether the on-screen age gaps prompt and encourage the off-screen ones, or vice-versa, is a bit of a chicken-and-egg issue. The point is that they both come down to the fact that it still seems to be ultimate alpha-male fantasy to date women young enough to be one’s daughter.

Every single one of the movies listed above – from Oliver Stone's Alexanderto Robert Zemeckis' Forrest Gump– was directed by a man. Of course, there are very occasionally movies about the potential sexiness of older women. Rewind to The Graduate. Unfortunately, that ultimate older woman, Anne Bancroft, was older than Dustin Hoffman by a mere five years. Next to Woody, Jack, Mel and Johnny, Bancroft's leap should hardly be worth noting. Instead it is taken as a cornerstone of cinema.

But then, going back to the original dog-years equation, that would be a gap of 35 years. That's almost up to Jack Nicholson's standards. – ( Guardiansevice)