second childhood vs senescence

second childhood

noun
  • The period or state of cognitive decline of an elderly person, characterized by childlike judgment and behavior. 

  • A childlike state in any adult, resulting from mental illness, trauma, or other conditions. 

senescence

noun
  • The state or process of ageing, especially in humans; old age. 

  • Old age; accumulated damage to macromolecules, cells, tissues and organs with the passage of time. 

  • Fruit senescence, leading to ripening of fruit. 

  • Ceasing to divide by mitosis because of shortening of telomeres or excessive DNA damage. 

  • Condition when the cell ceases to divide. 

How often have the words second childhood and senescence occurred in a corpus of books? (source: Google Ngram Viewer )