older vs elderly

older is not a noun while elderly is a noun.

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

As adjectives, older and elderly are synonyms defined as:

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

Other synonyms of older include aged, senior.

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

older (adjective)	elderly (adjective)
skilled through long experience	advanced in years; (`aged' is pronounced as two syllables)
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