boyish

adjective2

1. •
   Like a stereotypical boy in appearance or demeanor.

   • People disliked his boyish and juvenile behaviour.
   • Her boyish figure belied her femininity.
2. •
   Relating to a boy, or occurring in boyhood.

   • For Memnon […] fought hand to hand with his overmatch, and met his boyish and most dolorous death beneath the walls of Troy. — 1852