40 Year Old Vs 65 Year Old American Hitting 90

[Wolfram]

I imagine this could be solved mathematically.

Let f(x) be a function of the average life expectancy of an american male, where x is the year.

Let g(x) be the death rate for american males in one year where x is the age.

Find out where the two functions intersect. If it's > 40 years then you chose the 65 year old.

This is probably wrong and oversimplified but someone who's better at math should be able to solve this.