antediluvian vs senior citizen

antediluvian and senior citizen both are nouns.

Word	Noun	Adjective	Verb	Adverb
antediluvian	Yes	Yes	No	No
senior citizen	Yes	No	No	No

As nouns, senior citizen is a hypernym of antediluvian; that is, senior citizen is a word with a broader meaning than antediluvian:

Other hypernyms of antediluvian include golden ager, old person, oldster.

antediluvian (noun)	senior citizen (noun)
a very old person	an elderly person
any of the early patriarchs who lived prior to the Noachian deluge

antediluvian (adjective)	senior citizen (adjective)
of or relating to the period before the biblical flood
so extremely old as seeming to belong to an earlier period