leading man vs adult male

leading man and adult male both are nouns.

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

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

Other hypernyms of leading man include actor, histrion, player, role player, thespian, man.

leading man (noun)	adult male (noun)
actor who plays the leading male role	an adult person who is male (as opposed to a woman)