Nearly 40 percent of the American workforce has a younger boss (a number that is growing quickly), but hereās a scary set of stats. When leadership development adviser Jack Zenger reviewed the seventeen thousand worldwide leaders who had gone through his leadership training program, he found the average age was forty-two. And yet the typical individual in these companies had become a supervisor at around age thirty and remained in that role for nine yearsāthat is, until age thirty-nineābut had never received any other training prior to Zengerās program. Thatās a dirty dozen years between thirty and forty-two during which young managers are running the orchestra pit without any formal guidance.