curmudgeon vs old person

curmudgeon and old person both are nouns.

Word	Noun	Adjective	Verb	Adverb
curmudgeon	Yes	No	No	No
old person	Yes	No	No	No

As nouns, old person is a hypernym of curmudgeon; that is, old person is a word with a broader meaning than curmudgeon:

curmudgeon: a crusty irascible cantankerous old person full of stubborn ideas
old person: an elderly person

Other hypernyms of curmudgeon include golden ager, oldster, senior citizen.

curmudgeon (noun)	old person (noun)
a crusty irascible cantankerous old person full of stubborn ideas	an elderly person