ageing vs octogenarian

ageing

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

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

octogenarian

noun
  • Synonym of eightysomething: a person between 80 and 89 years old. 

adj
  • Of or related to eightysomethings. 

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