over-the-hill vs superannuated

over-the-hill and superannuated both are adjectives.

Word	Noun	Adjective	Verb	Adverb
over-the-hill	No	Yes	No	No
superannuated	No	Yes	No	No

As adjectives, over-the-hill and superannuated are synonyms defined as:

Other synonyms of over-the-hill include overage, overaged.

over-the-hill (adjective)	superannuated (adjective)
too old to be useful	old; no longer valid or fashionable
	too old to be useful