immature vs of age

immature

noun
  • An immature member of a species. 

adj
  • Not fully formed or developed; not grown. 

  • Childish in behavior; juvenile. 

of age

prep
  • Old enough to be considered an adult (in law, or by society generally). 

  • Having existed for a certain period of time; used in referring to a person's age. 

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