centenarian vs old as the hills

centenarian

adj

  • Aged 100 years or more; extremely old. 

  • Of or relating to centenarians or a centenary celebration. 

noun

  • One who or that which is at least 100 years old. 

old as the hills

adj

  • Extremely old. 

How often have the words centenarian and old as the hills occurred in a corpus of books? (source: Google Ngram Viewer )