Many executives joke about being carried from the office in a box; few earn that right. Malcolm McAlpine was still involved in the day-to-day running of the construction company Sir Robert McAlpine at his death last week, aged 93 – 75 years after he joined the business.

His is a family company, where blood is often thicker than governance. Generally, executives get far less time to prove their worth. On average, according to a study just out, chief executives who left the world’s 2,500 largest public companies in 2010 had been in office for 6.6 years, having been appointed aged 52. In 2000, when Booz & Co, the consultancy, carried out the first such annual survey, CEOs were two years younger when appointed but spent 8.1 years in the job. Even in the listed sector, however, there are exceptions. Warren Buffett, 80, springs to mind but GovernanceMetrics International identifies 15 other CEOs worldwide who are as old, or older, up to Walter Zable, 95-year-old founder-CEO (and director for six decades) of Cubic Corporation, the US defence and transport technology company.

What is the ideal age and tenure for a chief executive? The boss of one large US industrial company, in office since 2005, told me that