old codger vs Methuselah

old codger and Methuselah both are nouns.

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

As nouns, Methuselah is a hypernym of old codger; that is, Methuselah is a word with a broader meaning than old codger:

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

Other hypernyms of old codger include graybeard, greybeard, old man.

old codger (noun)	Methuselah (noun)
used affectionately to refer to an eccentric but amusing old man	(Old Testament) a patriarch (grandfather of Noah) who is said to have lived 969 years
	a man who is very old