lifespan vs senility

lifespan

noun
  • Some clams have lifespans far longer than those of human beings. 

  • The length of time for which an organism lives. 

  • The length of time for which something exists or is current or valid. 

senility

noun
  • The losing of memory and reason due to senescence. 

  • Senescence; the bodily and mental deterioration associated with old age. 

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