firmness vs immaturity

firmness

noun
  • security; steadfastness; good grip 

  • strictness; mental strength 

  • physical durability; rigidness (of material) 

immaturity

noun
  • Youth; the condition of being immature or not fully grown 

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