octogenarian vs past one's prime

octogenarian

adj
  • Of or related to eightysomethings. 

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

past one's prime

prep
  • No longer in an ideal condition. 

How often have the words octogenarian and past one's prime occurred in a corpus of books? (source: Google Ngram Viewer )