ageing vs septuagenarian

ageing

adj
  • UK, Australia, and New Zealand standard spelling of aging. 

noun
  • UK, Australia, and New Zealand standard spelling of aging. 

septuagenarian

adj
  • Of or related to seventysomethings. 

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

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