Cheekbones, check. Pout, check. Whippet-thin body, check. At first glance the latest crop of models don't seem like they stray from the fashion business's usual beauty rules, but look closer and it's clear something has shifted on the catwalks.

Models such as Stella Tennant and Agyness Deyn have been a staple of magazine covers for years, but model bookers are now taking this androgynous aesthetic a step further.

Ford models has signed Casey Legler, a bequiffed 35-year-old woman with a cheerful gap-toothed grin and razor-sharp cheekbones – to model menswear.

Brazilian transsexual model Lea T on the catwalk in Rio. Photograph: Felipe Dana/AP

The trend started with Lea T, a transsexual model who became the face of Givenchy, made the cover of Elle – and was soon pictured snogging Kate Moss for Love magazine. The distinctive Brazilian started modelling women's fashion while still physically male and, by the time she underwent sex reassignment surgery last year, was already a fixture in the fashion world. The first internationally successful transsexual model, she was photographed naked for Vogue, hiding her male genitals with her hand. But as someone who identifies herself as a woman, her place in women's fashion magazines is hardly a surprise.

Andrej Pejic modelling for Jean Paul Gaultier. Photograph: Pascal Le Segretain/Getty Images

But then came the delicately featured Andrej Pejic. The Bosnian started out as a male model, but was soon modelling women's clothes for designers including Jean Paul Gaultier. This year he opened a show in a wedding dress at Barcelona's bridal week.

Following hot on his high heels is Ukrainian Stav Strashko who made waves in a red bikini when he starred in a Toyota advert. Legler, a former Olympic swimmer, told Time that Pejic's success has opened the door for models cross-dressing. "This is a unique little moment that fashion is allowing to have happen," she says. Although celebrities have been on the trend for slightly longer – it's been two years since Tilda Swinton modelled menswear for Pringle.

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Stealing all the limelight now, meanwhile, is the Voguing Chinese grandfather Liu Xianping who at the age of 72 is reported to have said he was helping his granddaughter unpack her stock for her online fashion store when he started giving her advice on how to style the clothes. The playful photographs of him modelling her wares have become an online sensation – and apparently increased sales five-fold.

Liu Xianping, 72-year-old Chinese male model. Photograph: Lu Tin/AFP/Getty Images

So what's behind this new appetite for the androgynous look? Is it a sign the fashion world is opening its arms to reflect the diversity of our bodies – or just the latest fad to provide shock value now Crystal Renn has lost weight?

Legler herself thinks it is a way of exposing how stifling strict gender roles can be: "We have very strict ways in which we identify ourselves as men or women and I think that those can sometimes be limiting … Seeing me on the men's board … speaks to a notion of freedom, you know. There's something really bold about that … it's saying there is also this other way and it's really rad."

But social commentator Bidisha says she is sceptical about the idea that the models suggest the industry is increasingly willing to soften its strict standards of beauty. "I love fashion, style and design but I am cynical about the fashion industry. They will do whatever results in a cultural buzz that will turn into sales and money. What fashion says is: 'You can be transsexual, you can be androgynous, you can be old, you can be young, you can be larger than a size 12 but you must still be as beautiful as all the other models.' Their wallet lives on the side of the status quo."