young person vs pupil

young person and pupil both are nouns.

Word	Noun	Adjective	Verb	Adverb
young person	Yes	No	No	No
pupil	Yes	No	No	No

As nouns, pupil is a hyponym of young person; that is, pupil is a word with a more specific, narrower meaning than young person:

Other hyponyms of young person include blade, hobbledehoy, pup, puppy, school-age child, schoolchild, slip.

young person (noun)	pupil (noun)
a young person (especially a young man or boy)	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)