(FORTUNE Magazine) – In spite of an infusion of younger chief execs -- the youngest is Michael Dell, 27, founder of Dell Computer -- the average age of a FORTUNE Industrial 500 CEO is 57 years, 4 months, basically unchanged since the late 1960s. The reason, according to Eugene Jennings, professor emeritus of business management at Michigan State University: An increasing number of CEOs are outsiders who move into the top job at riper ages than their counterparts of yore. In 1991, for example, directors of Goodyear Tire & Rubber hired Stanley Gault at 65 after his retirement as CEO of Rubbermaid. Some silver hairs are home grown. Harold ''Red'' Poling moved up from vice chairman to CEO of Ford Motor at 64. His likely heir: Alex Trotman, 59, head of Ford's North American operations. The heads of service firms are a slightly sprightlier bunch at an average of 55 years, 6 months. Says Jennings: ''Industrials are slower to change. Since the Seventies their chiefs have been very conservative and produced replacements very much in their own image.'' Those looking for youth in a boss should turn to FORTUNE's list of the 100 fastest-growing companies (October 5, 1992). Their chief executives average 49 years, 2 months. -- R.T.