Answer:
senescence
Explanation:
Spencer, who is 55 years old, didn't realize how much his physical appearance had changed until he saw a picture of himself taken 20 years ago. Spencer's gradual change in physical appearance was due to senescence. Senescence is the gradual deterioration of functional attributes with age, it is the deteriorating process following maturity that leads to natural aging and then death. Senescence is an irreversible growth growth and aging of cells.
