If I'm not mistaken there's a "life expectancy" parameter in the descr_campaign.xml file. Again, I *think* that past said age, generals have a set % chances to snuff it each turn (this seems to be hardcoded though, never found anything regarding this in any file). Or perhaps the parameter just sets the maximum age generals can ever get (not at home, can't check for sure).
Still, it's better than vanilla MTW1, where generals died at 61, all of them :) (and even with the last patch, generals dead from old age were replaced with a new one with the exact same stats :/ )