young man vs adult male

young man and adult male both are nouns.

Word	Noun	Adjective	Verb	Adverb
young man	Yes	No	No	No
adult male	Yes	No	No	No

As nouns, adult male is a hypernym of young man; that is, adult male is a word with a broader meaning than young man:

Other hypernyms of young man include adolescent, stripling, teen, teenager, man.

young man (noun)	adult male (noun)
a teenager or a young adult male	an adult person who is male (as opposed to a woman)