Boardroom age: only a number? Petrolheads may quibble, but German cars have an enviable reputation for durability. The same could be said of Ferdinand Piëch, former chief executive and now supervisory board chairman of Volkswagen, the country's largest carmaker. Talk that the 76-year-old - who stepped in to drive the revival in VW's fortunes two decades ago - might retire brought swift denials this week. "Those who are reputed to be dead, live longer," a German news site quoted him as saying. VW has long defied many corporate governance norms, and few investors would quarrel with Mr Piëch's achievement in building today's juggernaut. But the episode throws a rare spotlight on the issue of age in boardrooms. This has had a lower profile than the heated debate over gender balance and female quotas. Yet studies suggest that changes are occurring rapidly, with boardrooms greying and companies shying away from constraints. Take a recent Korn Ferry Institute report on Canada's top 300 groups. This found that, in 1997, 8 per cent of directors were 71 or older. By 2010, that figure had risen to 15 per cent. The percentage in the 61-70 band jumped from 39 per cent to 45 per cent. An earlier KF study, meanwhile, showed that the number of North American companies that had a mandatory retirement age for directors fell from almost four-fifths in 1998, to two-thirds by 2007. In the UK and Japan, the proportion was even lower. As for those groups that did impose restrictions, the cut-off ages averaged from as low as 65 in Japan to 72 in North America. It can, of course, be argued that today's 70 is yesterday's 50. The paucity of high-quality non-executive directors may also make companies loath to lose good candidates. And using term limits to revitalise board composition may make more sense than cut-off ages - although for older directors this can amount to much the same thing. But if one argument for board gender diversity is that women bring different viewpoints, the same can surely be said for some careful age variety. Look no further than VW. Its succession planning may be a touchy matter, but board age diversity cannot be faulted. It ranged from 36 to 81 at the end of 2012.