young and inexperienced
callow - immature
A person, particularly one who is young or new to something, who behaves or speaks in a way that shows little in the way of confidence, judgement, or experience, can be described as ‘callow’. This word is generally used to express disapproval and is often followed by the noun ‘youth’.
I was just a callow youth when I first joined the company, but luckily I had a mentor who could show me the ropes.
That wily businessman used a number of tricks of the trade to secure himself a favourable deal. Unfortunately, our inexperienced negotiator was too callow to recognise them.
Many feel that Emily is too young and callow to take on such responsibility, but she is a lot more mature than people give her credit for.