centenarian vs senescent

centenarian

adj
  • Aged 100 years or more; extremely old. 

  • Of or relating to centenarians or a centenary celebration. 

noun
  • One who or that which is at least 100 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 centenarian and senescent occurred in a corpus of books? (source: Google Ngram Viewer )