juvenile

Adjective

• displaying or suggesting a lack of maturity
  • adolescent insecurity
    
  • jejune responses to our problems
    
  • their behavior was juvenile
    
  • puerile jokes
    

• of or relating to or characteristic of or appropriate for children or young people
  • juvenile diabetes
    
  • juvenile fashions
    

Noun

• a young person, not fully developed

Related words

• Synonyms: 
  adolescent , jejune , puerile , juvenile person
• Antonyms: 
  adult , grownup