twenty-four vs xxiv

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

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

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

Other synonyms of twenty-four include 24.

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

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