old woman vs old person

old woman and old person both are nouns.

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

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

Other hypernyms of old woman include golden ager, oldster, senior citizen, adult female, woman.

old woman (noun)	old person (noun)
a woman who is old	an elderly person
herb with greyish leaves found along the east coast of North America; used as an ornamental plant