ONE much-discussed cause of the Jasmine Revolution in the Arab world is the age difference between youthful populations and grizzled leaders. Egypt’s median age is 24. President Hosni Mubarak was the fifth-oldest leader in the world before he was toppled aged 82. The countries in the chart below suggest that such a wide gap is more common in autocracies like Saudi Arabia, Yemen, Algeria, Cuba and North Korea (where Kim Jong Il celebrates his 70th birthday on February 16th). Democracies, by contrast, seem to prefer more youthful leaders these days, though India and Italy are exceptions to this trend.