age vs decrepitude

age and decrepitude both are nouns.

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

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

age: a late time of life
decrepitude: The quality or state of being wasted and weakened by or as if by the infirmities of old age.

Other hyponyms of age include dotage, second childhood, senility, autumn years.

age (noun)	decrepitude (noun)
how long something has existed	a state of deterioration due to old age or long use
a time of life (usually defined in years) at which some particular qualification or power arises	The quality or state of being wasted and weakened by or as if by the infirmities of old age.
a late time of life
an era of history having some distinctive feature
a prolonged period of time