hang up one's boots vs superannuate

hang up one's boots

verb
  • retire, call it a day 

superannuate

verb
  • To retire due to age. 

  • To retire or put out of use due to age. 

  • To give a pension to, on account of old age or other infirmity; to cause to retire from service on a pension. 

  • To show to be obsolete due to age. 

  • To become obsolete or antiquated. 

How often have the words hang up one's boots and superannuate occurred in a corpus of books? (source: Google Ngram Viewer )