pupil vs youth

pupil and youth both are nouns.

Word	Noun	Adjective	Verb	Adverb
pupil	Yes	No	No	No
youth	Yes	No	No	No

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

Other hypernyms of pupil include spring chicken, young person, younker.

pupil (noun)	youth (noun)
the contractile aperture in the center of the iris of the eye; resembles a large black dot	the freshness and vitality characteristic of a young person
a learner who is enrolled in an educational institution	young people collectively
a young person attending school (up through senior high school)	a young person (especially a young man or boy)
	early maturity; the state of being young or immature or inexperienced
	the time of life between childhood and maturity
	an early period of development