In Hollywood, 40 is definitely the new 30

The acclaim from the movie The Wrestler did more than simply win Marisa Tomei the smattering of high-profile roles she's promoting this month: with that role, she was seen to champion the middle-aged woman in youth-obsessed Hollywood.

Marisa Tomei and her successful acting career make a case against Hollywood ageism.

The much-loved movie The Wrestler had plenty of things going for it. Mickey Rourke's gutsily brilliant performance as a vulnerable fighter down on his luck. Darren Aronofsky's sensitive direction. A refreshingly open ending.

But behind it all was the rare spectacle of a woman in her 40s dominating every scene in which she appeared.

Marisa Tomei fully deserved her Best Supporting Actress Oscar nomination for her performance as an exotic dancer whose rapport with wrestler Rourke is both harsh and tender. It kick-started a career that was perilously close to stagnating. But the acclaim did more than simply win Tomei the smattering of high-profile roles she's promoting this month. Hollywood is obsessed with youth, and dismissive of middle-aged women. Tomei, with that performance, asked why.

"Late-blooming" is surely one of the most patronising pronouncements upon an actor's career, especially when the object of such an epithet is a woman. In Tomei's case, the accusation is not strictly true, either: in 1992, she won an Academy Award at age 28 for her role as Joe Pesci's gum-chewing, wise-cracking fiancée in My Cousin Vinny. Nine years later, she was nominated again in Todd Field's crime drama In the Bedroom. But in between, there were duds aplenty. The least said about the tragic remake of Alfie, in which she starred opposite a risible Jude Law, the better.

So it's encouraging that, at the age most actresses are somewhat despicably approaching their sell-by date as far as Hollywood is concerned, Tomei is making a serious comeback. In Crazy, Stupid, Love - which last week The National called "an upscale adult comedy with something to say about marriage and commitment" - she quietly shines in a supporting role as a teacher finally seduced by Steve Carrell's somewhat awkward character.

This year's Venice Film Festival opened to The Ides of March, George Clooney's eagerly awaited political thriller in which Tomei plays an investigative reporter. And next week, she's on Broadway in a one-off reading of Dustin Lance Black's play 8, alongside Rob Reiner and Morgan Freeman. That's not all: plans for 2012 include co-starring with Alec Baldwin in an indie flick about a rock journalist called Lucky Them.

What's interesting about all these projects is that Tomei's characters are so diverse. She's not playing diluted versions of her role in The Wrestler over and over again. The acceptance that some of the best performances of recent times have come from fortysomething actresses with something to prove has been hard-won. But Tomei has opened the floodgates.

In the same year as Tomei's Wrestler nomination, 48-year-old Melissa Leo - brilliant as a compulsive gambler in Frozen River - was shortlisted in the Best Actress category. And two years later, while Mark Wahlberg and Christian Bale garnered most of the advance publicity for their participation in The Fighter, it was Leo's quietly remarkable turn as their mother that provided many of the stand-out scenes in David O Russell's boxing film. Her Oscar for Best Supporting Actress was richly deserved.

In 2009, Sandra Bullock won the Oscar for Best Actress at 44, summoning up the kind of tough yet endearingly realistic performance in The Blind Side of which many thought she was no longer capable.

Still, it's a little early to congratulate Hollywood for cleansing itself of ageism. At this year's Oscars, the Best Actress gong went to the impossibly young-looking Natalie Portman, despite Annette Bening's career-defining portrayal of a mother in a same-sex relationship in The Kids Are All Right. Quite rightly, Oscars are not given on sentiment. But in an industry that rarely likes to cast its gaze on middle-aged women, the fact that Bening and Julianne Moore were captivating and convincing in a film set in that world deserved to be further recognised.

So it'll be fascinating to see how the likes of Nicole Kidman (44), Cate Blanchett (42) and Naomi Watts (42) are treated by the Hollywood establishment in the years to come. Kidman, for example, played a thirtysomething mother in her most impressive recent film, Rabbit Hole. Should we be encouraging such behaviour if Kidman can pull it off, or decrying her for not using her considerable influence to lobby for more satisfying films about fortysomethings?

Difficult questions indeed. Still, at least Tomei would appear to have one future role in the bag. When Lady Gaga was asked by an American satellite radio station, Sirius, whom she would like to play her 24-year-old self in a biopic, she plumped for Tomei. "All my friends call me Marisa when I get angry," explained the 25-year-old, in a reference to Tomei's breakthrough performance in My Cousin Vinny.

Proof, then, that age should be no barrier.