octogenarian vs senescent

octogenarian

adj
  • Of or related to eightysomethings. 

noun
  • Synonym of eightysomething: a person between 80 and 89 years old. 

senescent

adj
  • Characteristic of old age. 

  • That ceases to divide. 

  • Growing old; decaying with the lapse of time. 

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