old vs gaga

old is a noun but gaga is not a noun.

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

old (noun)	gaga (noun)
past times

old (adjective)	gaga (adjective)
of long duration; not new	intensely enthusiastic about or preoccupied with
(used especially of persons) having lived for a relatively long time or attained a specific age	mentally or physically infirm with age
skilled through long experience
(used for emphasis) very familiar
excellent
just preceding something else in time or order
belonging to some prior time