juvenile vs someone

juvenile and someone both are nouns.

Word	Noun	Adjective	Verb	Adverb
juvenile	Yes	Yes	No	No
someone	Yes	No	No	No

As nouns, someone is a hypernym of juvenile; that is, someone is a word with a broader meaning than juvenile:

juvenile: a young person, not fully developed
someone: a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

Other hypernyms of juvenile include individual, mortal, person, somebody, soul.

juvenile (noun)	someone (noun)
a young person, not fully developed	a human being; person, singular, assertive existential pronoun; pronoun, person, singular; quantifier: assertive existential

juvenile (adjective)	someone (adjective)
of or relating to or characteristic of or appropriate for children or young people
displaying or suggesting a lack of maturity