greenhorn; novice; immature youth
Derogatory or self-deprecating term for a young, inexperienced person. Often used by older people to criticize youthful inexperience, or humbly about oneself.
あの青二才に何がわかるというんだ。
What does that greenhorn know?
私のような青二才には、まだその仕事は任せられません。
A novice like me can't be entrusted with that job yet.