elderly vs older

elderly is a noun but older is not a noun.

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

As adjectives, elderly and older are synonyms defined as:

elderly and older: advanced in years; (`aged' is pronounced as two syllables)

Other synonyms of elderly include aged, senior.

elderly (noun)	older (noun)
people who are old collectively

elderly (adjective)	older (adjective)
advanced in years; (`aged' is pronounced as two syllables)	skilled through long experience
	advanced in years; (`aged' is pronounced as two syllables)
	used of the older of two persons of the same name especially used to distinguish a father from his son