greybeard vs Methuselah

greybeard and Methuselah both are nouns.

Word	Noun	Adjective	Verb	Adverb
greybeard	Yes	No	No	No
Methuselah	Yes	No	No	No

As nouns, greybeard and Methuselah are synonyms defined as:

Other synonyms of greybeard include graybeard, old man.

greybeard (noun)	Methuselah (noun)
a stoneware drinking jug with a long neck; decorated with a caricature of Cardinal Bellarmine (17th century)	(Old Testament) a patriarch (grandfather of Noah) who is said to have lived 969 years
a man who is very old	a man who is very old