senescence

Short definition from Wiktionary

Noun

1. 1
   The state or process of ageing, especially in humans; old age.
2. 2
   Ceasing to divide by mitosis because of shortening of telomeres or excessive DNA damage.
3. 3
   Old age; accumulated damage to macromolecules, cells, tissues and organs with the passage of time.
4. 4
   Fruit senescence, leading to ripening of fruit.
5. 5
   Condition when the cell ceases to divide.