preadolescence vs salad days

preadolescence

noun
  • The period between childhood and adolescence, between the ages of about 9 and 11 for girls, and 10 and 12 for boys. 

salad days

noun
  • A period of inexperienced youthful innocence accompanied by enthusiasm and idealism. 

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