From this Scientific American article, Muscle Mass Beats BMI as Longevity Predictor:
“Researchers analyzed BMI and muscle mass data from more than 3,600 seniors in a long-term study. And they tracked which seniors had died, a decade later. Turns out BMI wasn't much good at predicting chance of death.
But muscle mass was: more muscle meant better odds of survival.”
BMI is a dubious measurement to begin with. Pictured is Mike Tyson. According to BMI charts he would be classified as clinically obese. He is not fat and has substantial muscle mass.