infancy vs one's salad days

infancy

noun
  • An early stage in the development of anything. 

  • The state of being a minor. 

  • The state of being an infant. 

  • The earliest period of childhood (crawling rather than walking). 

one's salad days

How often have the words infancy and one's salad days occurred in a corpus of books? (source: Google Ngram Viewer )