So you'll have 10-14 months of playtime until your character dies of old age (if you haven't spirit walked at all), but how exactly does that work? Does my character just have a random chance to permanently die after 10 months? Does a combination of more frequent diseases and more difficult spirit walking make it highly improbable to survive beyond 14 months?
You will have an amount of spirit. Age, deaths and diseases will decrease your spirit until 0 when you permanent die, meaning your soul cannot go back to your body and it will return to the Akashic Records.