twenty-nine vs xxix

twenty-nine is a noun but xxix is not a noun.

Word	Noun	Adjective	Verb	Adverb
twenty-nine	Yes	Yes	No	No
xxix	No	Yes	No	No

As adjectives, twenty-nine and xxix are synonyms defined as:

Other synonyms of twenty-nine include 29.

twenty-nine (noun)	xxix (noun)
the cardinal number that is the sum of twenty-eight and one

twenty-nine (adjective)	xxix (adjective)
being nine more than twenty	being nine more than twenty