past one's prime vs septuagenarian

past one's prime

prep
  • No longer in an ideal condition. 

septuagenarian

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

adj
  • Of or related to seventysomethings. 

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