septuagenarian vs seventysomething

septuagenarian

noun

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

adj

  • Of or related to seventysomethings. 

seventysomething

noun

  • A person between 70 and 79 years old. 

num

  • An indeterminate value between 70 (inclusive) and 80 (exclusive). 

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