older vs old

older is not a noun while old is a noun.

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

As adjectives, older and old are synonyms defined as:

older (noun)	old (noun)
	past times

older (adjective)	old (adjective)
skilled through long experience	of long duration; not new
advanced in years; (`aged' is pronounced as two syllables)	(used especially of persons) having lived for a relatively long time or attained a specific age
used of the older of two persons of the same name especially used to distinguish a father from his son	skilled through long experience
	(used for emphasis) very familiar
	excellent
	just preceding something else in time or order
	belonging to some prior time