WordNet sense 1 (a juvenile between the onset of puberty and maturity):

stripling, teen, teenager

WordNet sense 2 (being of the age 13 through 19):

teenage, teenaged

WordNet sense 3 ((used of living things especially persons) in an early period of life or development or growth):

young

WordNet sense 4 (displaying or suggesting a lack of maturity):

jejune, juvenile, puerile