Go to the "Global Enchantment" screen that is associated with the lab. ( I believe it is the 2nd from the Right ). It should list the spell "Burden of Time".

Then look up the spell "Burden of Time" in the spell index. You should find all your answers there. In order to stop the rapid aging and death of your troops you will need to dispel the Global Enchantment, or defeat the pretender who has cast the enchantment.