old vs rusty

old is a noun but rusty is not a noun.

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

old (noun)	rusty (noun)
past times

old (adjective)	rusty (adjective)
of long duration; not new	of the brown color of rust
(used especially of persons) having lived for a relatively long time or attained a specific age	ancient
skilled through long experience	covered with or consisting of rust
(used for emphasis) very familiar	impaired in skill by neglect
excellent
just preceding something else in time or order
belonging to some prior time