second childhood vs youngness

second childhood

noun
  • A childlike state in any adult, resulting from mental illness, trauma, or other conditions. 

  • The period or state of cognitive decline of an elderly person, characterized by childlike judgment and behavior. 

youngness

noun
  • The state or qualities of being young or youthful; youth. 

How often have the words second childhood and youngness occurred in a corpus of books? (source: Google Ngram Viewer )