Your time is approaching. Your body isn't what it used to be, and what's worse, neither is your mind. The trait is used every time you try any physically demanding tasks, or roll a physical save. Every tenth gaming session, this trait gets one step worse, and once it's at -5, you and the GM decide on a good scene and moment for your character to draw their last breath. Do note that the species have different lifespans, so read the race descriptions to find what counts as old for your species.
Should a significant period of in-game time pass between sessions, accelerate this trait accordingly.