schoolboy vs adult male

schoolboy and adult male both are nouns.

Word	Noun	Adjective	Verb	Adverb
schoolboy	Yes	No	No	No
adult male	Yes	No	No	No

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

Other hypernyms of schoolboy include boy, male child, man, pupil, school-age child, schoolchild.

schoolboy (noun)	adult male (noun)
a boy attending school	an adult person who is male (as opposed to a woman)