Out of game question: From what I gather, it's about five years per turn added, and there's nothing that can protect your units from it, right?
Can a unit die "in between turns" due to age, or does it still have to get diseased before and then loses just 1HP per month? If I might ask
(and searching the forum for "burden of time" showed me that a certain player seems to have a preference for this Global *g*)