doddering vs septuagenarian

doddering

adj
  • mentally or physically infirm due to old age; senile 

noun
  • A shaking or trembling movement, as of old age. 

septuagenarian

adj
  • Of or related to seventysomethings. 

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

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