old vs hoary

old is a noun but hoary is not a noun.

Word	Noun	Adjective	Verb	Adverb
old	Yes	Yes	No	No
hoary	No	Yes	No	No

old (noun)	hoary (noun)
past times

old (adjective)	hoary (adjective)
of long duration; not new	covered with fine whitish hairs or down
(used especially of persons) having lived for a relatively long time or attained a specific age	ancient
skilled through long experience	showing characteristics of age, especially having grey or white hair
(used for emphasis) very familiar
excellent
just preceding something else in time or order
belonging to some prior time