schoolboyish

/skulˌbɔɪɪʃ/
adjective
  1. Characteristic of or typical of a schoolboy, especially in being playful, mischievous, or immature.
    • He had a schoolboyish grin when he told the joke.
    • Her schoolboyish enthusiasm for video games surprised her coworkers.
    • The prank was a schoolboyish attempt to get attention.
Antonyms
What does "schoolboyish" mean? | whatsthatwordmean | whatsthatwordmean