college boy vs pupil

college boy and pupil both are nouns.

Word	Noun	Adjective	Verb	Adverb
college boy	Yes	No	No	No
pupil	Yes	No	No	No

As nouns, pupil is a hypernym of college boy; that is, pupil is a word with a broader meaning than college boy:

Other hypernyms of college boy include educatee, student.

college boy (noun)	pupil (noun)
a student (or former student) at a college or university	the contractile aperture in the center of the iris of the eye; resembles a large black dot
	a learner who is enrolled in an educational institution
	a young person attending school (up through senior high school)