college boy vs collegian

college boy and collegian both are nouns.

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

As nouns, college boy and collegian are synonyms defined as:

college boy and collegian: a student (or former student) at a college or university

Other synonyms of college boy include college man.

college boy (noun)	collegian (noun)
a student (or former student) at a college or university	a student (or former student) at a college or university