The US life expectancy for men is 76.4 years.
Half of 76.4 is 38.2 years
A third of 76.4 is 25.47 years
So middle age is 38.2 plus or minus 12.74 years
Young ===== Birth to 25.46 years
Middle Age = 25.46 to 50.94 years.
Old ======= 50.94 to 76.4 years
Questions?
