Expert

wet behind the ears

Meaning: immature or poor skill

Example: From the way the soldier handled the gun, everyone could tell that he was wet behind the ears. Read on

dab hand

a dab hand at Meaning and Synonyms: - expert - adept at - one skillful at - a person who is an expert at a particular activity - ... Read on

born yesterday

Meaning: naive; inexperienced

Example: Susan might look young, but she was not born yesterday. She is not going to fall for your lies. Read on