grandfather vs senior citizen

grandfather

noun
  • A father of someone's parent. 

  • A male forefather. 

  • The archived older version of a file that immediately preceded the father file. 

verb
  • To retain discontinued laws or rules for (a thing, person or organization previously affected by them). 

  • To be, or act as, a grandfather to. 

senior citizen

noun
  • An old person, variously considered to be a person over fifty, fifty-five, sixty, or sixty-five years of age. 

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