Until very recently, there was an unwritten rule in Hollywood that once an actress reached 40, the starring roles would magically dry up. While male actors kept on making action films and rom-coms into their 50s and 60s and were paired with ever-younger actresses, female stars were expected to recede into the woodwork once the bloom of youth began to fade.
Even huge stars like Elizabeth Taylor and Lauren Bacall were dropped like hot stones once they hit middle age. And while some actresses retired to avoid the ignominy of being snubbed by the industry, only the toughest and most talented women retained thriving film careers into middle and old age.
There are signs, however, that all of that has finally begun to change. A group of actresses now in their 40s have refused to fade away, and are out-earning stars 10 and 20 years younger than them. Actresses like Sandra Bullock, Julia Roberts, Jennifer Aniston and Nicole Kidman are continuing to land lead roles in big-budget movies, even romances and rom-coms, well into middle age.
Forty-eight-year-old Bullock scores consistently higher with the public than any other actress in opinion polls, and still earns $20m a picture. Her recent roles range from playing the novelist Harper Lee in Infamous to an Oscar-winning turn as a formidable southern businesswoman in The Blind Side. But she's also still considered a romantic lead, and in 2009 starred in one of the best rom-coms of recent times, The Proposal.
Later this year, she'll co-star with 42-year-old comedienne Melissa McCarthy in a buddy crime comedy called The Heat, playing exactly the sort of role that would always have gone to a sub-30-year-old in the past.
Cameron Diaz turns 41 in August and is still landing the kind of romantic roles that made her famous in the first place. She was recently paid $10m for co-starring with Tom Cruise in the action caper Knight and Day, and the same amount for providing the voice of Princess Fiona in Shrek Forever After. She looks great, too, and attributes her youthful looks to "exercise, healthy diet, lots of water, lots of laughter, lots of sex . . ."
Julia Roberts is 45 but still landing leading roles in films like Eat Pray Love and Mirror, Mirror, in which she played a memorably glamorous witch. Nicole Kidman is the same age, and gets roles that would traditionally have gone to considerably younger women. She was paid $13m to star in Baz Lurhmann's epic Australia.
These are not isolated cases. Naomi Watts, who's 44, earned an Oscar nomination last year for her portrayal of a heroic mother in The Impossible, while 46-year-old Halle Berry is still a sex symbol, and plays a glamorous 999 operation in The Call, a thriller which opens here later this year.
Forty-four-year-old Jennifer Aniston still holds her own in rom-coms, and earns $8m to $10m a film. Penelope Cruz is only 39, but is about to become the oldest Bond girl ever in Sam Mendes's eagerly awaited follow-up to Skyfall.
It's all a far cry from how things used to be in Hollywood. Back in the 1930s and 1940s, even the most famous actresses began looking nervously over their shoulders once they hit 30, and most ended up on the scrapheap once their studio decided they were past their prime.
Jean Arthur, for instance, was perhaps the biggest female romantic comedy star of the 1930s, and worked with Frank Capra and George Stevens in films such as Mr Smith Goes to Washington and Talk of the Town. Capra called her "one of the greatest comediennes the screen has ever seen", but that didn't stop Columbia from dumping her in the early 1940s.
Lana Turner became famous for playing femmes fatales in noir classics like The Bad and the Beautiful. But MGM gave her the cold shoulder once she hit 40.
Ava Gardner was an even bigger star in the 1940s and 1950s, her fame only enhanced by her stormy marriage to Frank Sinatra. But Ava was an out-and-out beauty, and they always ended up getting treated the worst. When her career began to flag in the 1960s, Gardner campaigned to play the role of Mrs Robinson in Mike Nichols' The Graduate.
It seemed perfect. Ava was then in her mid-40s but looking good, and spot-on casting one would have thought to play a married woman of similar vintage who seduces a young college graduate played by Dustin Hoffman. With a supreme irony, the producers decided to pick a younger woman, Anne Bancroft, who at 35 was only six years older than Hoffman.
Fey blonde Gloria Grahame won an Oscar for The Bad and the Beautiful and played memorable vamps in The Big Heat and It's a Wonderful Life. She was only 32 when a drinking problem and a reputation for being difficult saw her pushed out of the industry only three years after that Oscar-winning turn. She later disfigured herself through an obsession with plastic surgery and was dead by 57.
To studio bosses, there was nothing more expendable than a fading actress, and Marilyn Monroe's death was probably hastened by concerns over how she would exist as an actress once the glamour was gone.
There were exceptions, of course, but actresses like Bette Davis and Katharine Hepburn combined great talent with formidable determination and toughness. For most Hollywood actresses of the 1950s, 1960s, 1970s and even 1980s, the phone stopped ringing once the candles on their 40th birthday cakes were extinguished.
So what's changed?
Part of the reason for this mini-revolution is that older people now make up a larger part of the cinema-going public than they did a decade or two ago. More than one-third of all movie tickets sold in America last year were bought by people aged 40 or over, and that's an audience that likes its films more grown-up, and its actresses more mature.
A slightly less laudable reason for the continued success of Sandra Bullock and Jennifer Aniston is that they look a hell of a lot better than 40-somethings used to, thanks to dieting, exercise, wardrobe and the odd cosmetic tweak.
But in addition, Bullock, Roberts and Aniston in particular are too well liked by the public to be cast aside.
All three of those actresses can look forward with some confidence to enjoying the longevity of legends like Helen Mirren, Meryl Streep, Diane Keaton and Sally Field.
Till now, those stars have been very much the exceptions that proved the rule in a shamelessly sexist and youth-obsessed business, but maybe that's finally changing, perhaps for good.