senile vs old

senile is not a noun while old is a noun.

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

senile (noun)	old (noun)
	past times

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