octogenarian vs septuagenarian

octogenarian

adj
  • Of or related to eightysomethings. 

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

septuagenarian

adj
  • Of or related to seventysomethings. 

noun
  • Synonym of seventysomething: a person between 70 and 79 years old. 

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