Nouns

(n)juvenile, juvenile persona young person, not fully developed

Adjectives

(a)juvenileof or relating to or characteristic of or appropriate for children or young people“juvenile diabetes”, “juvenile fashions”
(s)adolescent, jejune, juvenile, pueriledisplaying or suggesting a lack of maturity“adolescent insecurity”, “jejune responses to our problems”, “their behavior was juvenile”, “puerile jokes”