auld langsyne vs old times

auld langsyne and old times both are nouns.

Word	Noun	Adjective	Verb	Adverb
auld langsyne	Yes	No	No	No
old times	Yes	No	No	No

As nouns, auld langsyne and old times are synonyms defined as:

Other synonyms of auld langsyne include good old days, lang syne, langsyne.

auld langsyne (noun)	old times (noun)
past times remembered with nostalgia	past times remembered with nostalgia