From Creatures Wikia
Ageing is a chemical in the original Creatures. It decays from the moment of birth and at certain points its reducing level triggers a change in life stage. The original intention was for death to occur when the chemical reached a very low point, but this was left out of the original genome and is only present in certain breeds - see life stage for further details. Ageing was replaced by the chemical Life in later games.
- Norn ~10 hours or indefinite