ろうすい老衰rousui
1.
The gradual decline in physical and mental health that occurs with advanced age, leading to a weakness or frailty in the elderly.
2.
A state of deterioration that does not stem from any specific illness, yet ultimately results in death as one ages.
3.
The process by which a person's body and mind weaken over time due to the natural effects of aging.
Example:
彼は老衰で二年前に亡くなった。