old vs older

old is a noun but older is not a noun.

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

As adjectives, old and older are synonyms defined as:

old (noun)	older (noun)
past times

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