infancy vs teen-ager

infancy

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

  • An early stage in the development of anything. 

  • The state of being a minor. 

  • The state of being an infant. 

teen-ager

noun
  • Dated spelling of teenager. 

How often have the words infancy and teen-ager occurred in a corpus of books? (source: Google Ngram Viewer )