old vs previous

old is a noun but previous is not a noun.

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

As adjectives, old and previous are synonyms defined as:

old (noun)	previous (noun)
past times

old (adjective)	previous (adjective)
of long duration; not new	too soon or too hasty
(used especially of persons) having lived for a relatively long time or attained a specific age	(used especially of persons) of the immediate past
skilled through long experience	just preceding something else in time or order
(used for emphasis) very familiar
excellent
just preceding something else in time or order
belonging to some prior time