juvenile juvenile /ˈdʒuːvəˌnaɪl/

adjective

1. () Of or relating to or characteristic of or appropriate for children or young people  ( juvenile )
   of or relating to or characteristic of or appropriate for children or young people
    Juvenile diabetes
   juvenile diabetes
    Juvenile fashions
   juvenile fashions
   
2. Displaying or suggesting a lack of maturity  ( adolescent , jejune , juvenile , puerile )
   displaying or suggesting a lack of maturity
    Adolescent insecurity
   adolescent insecurity
    Jejune responses to our problems
   jejune responses to our problems
    Their behavior was juvenile
   their behavior was juvenile
    Puerile jokes
   puerile jokes
   

noun

1. A young person, not fully developed  ( juvenile , juvenile person )
   a young person, not fully developed