old man vs old codger

old man and old codger both are nouns.

Word	Noun	Adjective	Verb	Adverb
old man	Yes	No	No	No
old codger	Yes	No	No	No

As nouns, old codger is a hyponym of old man; that is, old codger is a word with a more specific, narrower meaning than old man:

old man: a man who is very old
old codger: used affectionately to refer to an eccentric but amusing old man

Other hyponyms of old man include codger, antique, gaffer, old-timer, old geezer, oldtimer, patriarch.

old man (noun)	old codger (noun)
an informal term for your father	used affectionately to refer to an eccentric but amusing old man
a man who is very old
a familiar term of address for a man
(slang) boss
aromatic herb of temperate Eurasia and North Africa having a bitter taste used in making the liqueur absinthe