Cims are not real so it really doesn't matter, however, if one is looking at a realistic scenario, people get old and it varies from person to person on what age they die at, some may die at an early age, some live until they're a 100 years old.
In all sincerity, for every Cim over a specific age to die all at the same time give the impression it's the players fault whereas it may not be.
As I said in an earlier post, we have no info on how / why they died, was it old age, a serious illness, a plague of some kind or something else.?
If we knew the cause we could most probably fix it, either add more health buildings, increase police coverage etc.
But as it is we just have to guess.