youngness vs age

youngness and age both are nouns.

Word	Noun	Adjective	Verb	Adverb
youngness	Yes	No	No	No
age	Yes	No	Yes	No

As nouns, age is a hypernym of youngness; that is, age is a word with a broader meaning than youngness:

youngness (noun)	age (noun)
the opposite of oldness	how long something has existed
	a time of life (usually defined in years) at which some particular qualification or power arises
	a late time of life
	an era of history having some distinctive feature
	a prolonged period of time