matureness vs youth

matureness and youth both are nouns.

Word	Noun	Adjective	Verb	Adverb
matureness	Yes	No	No	No
youth	Yes	No	No	No

As nouns, youth is a hyponym of matureness; that is, youth is a word with a more specific, narrower meaning than matureness:

matureness: state of being mature; full development
youth: early maturity; the state of being young or immature or inexperienced

Other hyponyms of matureness include adulthood, ripeness, post-maturity, post-menopause.

matureness (noun)	youth (noun)
state of being mature; full development	the freshness and vitality characteristic of a young person
	young people collectively
	a young person (especially a young man or boy)
	early maturity; the state of being young or immature or inexperienced
	the time of life between childhood and maturity
	an early period of development