I've encountered a few posts relating to people having villagers mysteriously age and die suddenly because the computer's clock got changed. I have two solutions for that problem.
1) if you have to change the settings on your PC, pause the game FIRST. I did an experiment and confirmed that when I paused the game my villagers did not age - makes sense, right?

2) just in case, go into your date and time properties (right-click on the time on your taskbar on a PC - sorry I don't have a clue for MAC users). Go to the Internet Time tab and unclick "automatically synchronize with an Internet time server". that way your time won't change without your doing it deliberately.

Hope this helps some of you! I am so addicted to this game it's really sad...

Dar

While some people have had inadvertent trouble when they have set their system clock, most people with serious game problems are deliberately adjusting their system clocks to use what's know as the "time cheat." The real-time engine in Virtual Villagers is very dependent upon the system clock and will usually malfunction with repeated system clock adjustments.