If you're being juvenile, you're not acting your age. Unless of course you are a juvenile. In which case, carry on.

While the noun juvenile refers to someone not physically or emotionally mature, the word is often used as an adjective to refer to anything specifically for young people, such as juvenile reading materials or movies. It can be derisive, as in "Don't act so juvenile," suggesting a silliness unbecoming an adult. The word comes from the Latin juvenīlis, meaning "youthful" — similar, but much more flattering.

Definitions of juvenile

adj of or relating to or characteristic of or appropriate for children or young people

juvenile diabetes”
juvenile fashions”

adj displaying or suggesting a lack of maturity

“their behavior was juvenile
adolescent, jejune, puerile
characteristic of a lack of maturity

n a young person, not fully developed

juvenile person
adult, grownup
a fully developed person from maturity onward
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preteen, preteenager
a preadolescent boy or girl (usually between 9 and 12 years of age)
adolescent, stripling, teen, teenager
a juvenile between the onset of puberty and maturity
child, fry, kid, minor, nestling, nipper, shaver, small fry, tiddler, tike, tyke, youngster
a young person of either sex
an artless innocent young girl (especially as portrayed on the stage)
spring chicken, young person, younker, youth
a young person (especially a young man or boy)
a child: son or daughter
a dashing young man
a robust child
a child secretly exchanged for another in infancy
a Palestinian juvenile 10-15 years old who fights against the Israelis
child prodigy, infant prodigy, wonder child
a prodigy whose talents are recognized at an early age
foster child, foster-child, fosterling
a child who is raised by foster parents
an awkward bad-mannered adolescent boy
imp, monkey, rapscallion, rascal, scalawag, scallywag, scamp
one who is playfully mischievous
a young child
a British teenager or young adult in the 1960s; noted for their clothes consciousness and opposition to the rockers
a child who has lost both parents
a Mexican-American teenager who belongs to a neighborhood gang and who dresses in showy clothes
a young child who is small for his age
poster child
a child afflicted by some disease or deformity whose picture is used on posters to raise money for charitable purposes
kindergartener, kindergartner, preschooler
a child who attends a preschool or kindergarten
punk, punk rocker
a teenager or young adult who is a performer (or enthusiast) of punk rock and a member of the punk youth subculture
pup, puppy
an inexperienced young person
a teenager or young adult in the 1960s who wore leather jackets and rode motorcycles
pupil, school-age child, schoolchild
a young person attending school (up through senior high school)
a word used for misbehaving children
a young and slender person
a child
bambino, toddler, tot, yearling
a young child
poor and often mischievous city child
street child, waif
a homeless child especially one forsaken or orphaned
young buck, young man
a teenager or a young adult male
Type of:
individual, mortal, person, somebody, someone, soul
a human being

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