Apple Inc.’s new CEO joined the iPhone maker 25 years ago and was tapped for the top job at age 50. While that would have been a common trajectory for CEOs a generation ago, the typical path to power for business leaders is longer now, with more career twists and turns along the way. The average American CEO is 61, a decade older than in 2000. Tenure length and delayed retirement are only part of the story. Executives are starting in the top job later in life than they used to. The average age at appointment is now 55 years old, up from just under 48 years old in 2000. This graying of the corner office, shown in a National Bureau of Economic Research working paper that analyzed the hiring and career patterns of more than 50,500 CEOs in the U.S.…