xxiv vs twenty-four

xxiv is not a noun while twenty-four is a noun.

Word	Noun	Adjective	Verb	Adverb
xxiv	No	Yes	No	No
twenty-four	Yes	Yes	No	No

As adjectives, xxiv and twenty-four are synonyms defined as:

Other synonyms of xxiv include 24.

xxiv (noun)	twenty-four (noun)
	the cardinal number that is the sum of twenty-three and one

xxiv (adjective)	twenty-four (adjective)
being four more than twenty	being four more than twenty