1. wet behind the ears
From the way the soldier handled the gun, everyone could tell that he was wet behind the ears.
A 40 year old punk still wet behind the ears.
2. callow
She's just a callow teenager so you shouldn't expect too much.
Don't be angry with him, he's just a callow youth.
English word "young and inexperienced"(callow) occurs in sets:
English Advanced Adjectives