sexual maturity vs youth

sexual maturity

noun
  • The stage when an organism can reproduce, though this is dissimilar from adulthood. 

youth

noun
  • The part of life following childhood; the period of existence preceding maturity or age; the whole early part of life, from childhood, or, sometimes, from infancy, to adulthood. 

  • A young man; a male adolescent or young adult. 

  • The quality or state of being young. 

  • A young person. 

  • Young persons, collectively. 

How often have the words sexual maturity and youth occurred in a corpus of books? (source: Google Ngram Viewer )