幼稚
yoù zhì · HSK 7
childish
👶 幼 young + 稚 immature = doubly young, i.e. childish; yòu zhì sounds like yo-jr (a junior)
Both characters carry the sense of young: 幼 (yòu) is infant/young and 稚 (zhì) is immature/tender. Stacking two young-words pushes the meaning past mere age into puerile or childish behavior.