If you had to name the two most commonly repeated adages about films today, they’d probably be (a) there are almost no substantial roles for actresses over 35 and (b) only negligible numbers of people over 35 go to the cinema any more. In both cases, one feels, Meryl Streep never got the memo. This great American actress, who has won two Oscars and, astonishingly, has been nominated for 13 more, turned 60 last summer and is currently on her hottest career roll since the early 1980s. More remarkably, she is doing it with a series of light, amusing, mainstream films far removed from the worthy, serious roles (The Deer Hunter, Sophie’s Choice, Out of Africa) that characterised her early work. Streep’s successful late run began with The Devil Wears Prada (2006), in which she played a chilling, imperious fashion editor to great comic effect. It continued with the musical Mamma Mia! (2008), which cast her as a fetching, sun-kissed older woman, once the libertine lead singer of a girl group, now living on a Greek island. One could not imagine the younger Streep even considering the role; yet Mamma Mia! became the highest-grossing film ever released in Britain. Last year she excelled in the delightful Julie & Julia – clearly, she is having fun. Given her long, dazzling CV, she has nothing left to prove, and no longer needs to limit herself to solemn roles; she even injected a dose of dark humour into her portrayal of a vengeful nun in Doubt (2008).

Consequently, Streep has once again become the actress of choice for a generation of film audiences in her own age range. Mostly these are women, who see her in an example of how to act one’s age with not just grace but also intelligence, wit and exuberance. But I also know several men in that same demographic who admit to liking Streep more than then they ever did. I put it down to sex. Quite apart from her remarkable skills as a film actress, there’s a glow, a sensuality and a radiance about Streep these days. Put simply, she’s looking great. It’s no accident that sex is a prominent theme in her sharply witty new romantic comedy, It’s Complicated, a substantial hit in the States, where it has already grossed more than $60 million. It comes from writer-director Nancy Meyers, who has previously delivered bland, adult-friendly material such as Something’s Gotta Give and The Holiday, but moves up to a different league here. Streep plays Jane, an independent, divorced businesswoman on the verge of an affair with her architect (Steve Martin) at the very point that her ex-husband (Alec Baldwin) starts to find his interest in her becoming rekindled. Dishing the dirt with girl-friends over wine, Jane proclaims: “I have so much energy recently – probably as a result of all the sex I’ve been having. Turns out… I’m a bit of a slut.” I’ve sat with paying audiences twice over the Christmas period, watching the astute, appealing trailer for It’s Complicated, and they virtually cheer that scene. Think of it as a companion image to Streep in Mamma Mia!, clad in dungarees, with a light tan and her blonde, tousled hair cascading below her shoulders, bouncing joyously on her bed.

These two scenes are assertions of enduring sexuality, a means of signalling that once again the baby-boomer generation is dictating its own rules as it gets older – in this case, living out the exquisite little secret that you can be 60 and still have a splendid sex life – flying in the face of reactions along the lines of “Eeeeewww!” from their children. Streep isn’t the only actress of her generation to emerge as a mature sex symbol, of course. Helen Mirren and Susan Sarandon have long oozed sensuality on the big screen. And recently Sigourney Weaver told me she would love to star in a romantic comedy featuring two 60-year-olds. Still, Streep is the market leader, so to speak – and in her case, this late-blossoming aspect of her career feels like something of a personal liberation. I’ve met her several times over the years, and have always been struck by her humour. She is someone who, if she finds something amusing, lets you know it: she’ll throw her head back, give a full-throated laugh, and often slap her thigh for good measure. But for years this facet of her personality was missing in her film acting. She seemed too consumed by her own monumental technique (remember her flawless mastery of all those diverse accents?) to be seen to be enjoying herself. Those days are clearly over. And I suspect she is also now in a stage of her life where she feels carefree and less weighed down by responsibility. Streep has four grown children (aged 18 to 30) from her marriage to sculptor Don Gummer – they have been married for more than 30 years. About a decade ago, she told me that she had turned down several substantial roles because she wanted to be around to take care of her growing kids. For a long period, she would only accept work in and around her hometown, New York City, so she would not be apart from them in their school term time. The mind reels: in how many more Oscar ceremonies might she have competed, if not for those self-imposed rules?

Yet she and her husband now find themselves at an enviable stage of life: their children (the youngest is 18) are self-sufficient, and they are healthy and vigorous enough in their 60s to enjoy their independence. In her case, it shows: there’s a zest and verve to her work that not only suits her, but clearly suits her fans as well. It’s a rare talent who finds herself at the zenith of her popularity at the age of 60. But then the phrase “a rare talent” describes Meryl Streep to a tee.

‘It’s Complicated’ opens in the UK on Friday