Can we put an age limit on fashion when the ‘model of the year’ is only 17?

At last, leading designers and publishers have agreed to stop using models under the age of 18 in editorials and on the catwalk.

Francis Pinault, chief executive of the Kering Group which owns Gucci, Balenciaga, St Laurent and McQueen, made the commitment this week at a conference for the fashion industry in Copenhagen, along with the the Council of Fashion Designers of America. Kering is following Vogue publishers Conde Nast, which made a similar commitment last August. Yet in December Kaia Gerber, the daughter of former supermodel Cindy Crawford, was crowned "Model of the Year". She's just 17 and walked the catwalk in Stella McCartney’s show earlier this year.

Enforcing any kind of ruling is bound to be difficult, and the fashion industry is notorious for breaking rules. How can luxury brands square their mission with "sustainability"? The fashion business is predicated on persuading us to shop even when our wardrobes are already full.

Crown Princess Mary of Denmark was praised for wearing a "recycled" skirt from 2015 to the event, but she also turned up in a brand new McQueen blazer and an H&M dress – both companies were sponsors of the conference.

Staying on message is difficult in planet fashion.