According to [0], John Simmons became CEO in 1972 at age 53 and remained there until he stepped down for health reasons in 1980/81 (he died of cancer shortly thereafter) [1]

[0] https://www.nytimes.com/1972/11/16/archives/simmons-takes-mo...

[1] https://www.nytimes.com/1981/04/04/obituaries/john-w-simmons...