callow
adjective literary disapproving uk/ˈkæl.əʊ/ us/ˈkæl.oʊ/
（尤指年轻人）幼稚的;不自信的;不谙世事的
Someone, especially a young person, who is callow behaves in a way that shows they have little experience, confidence, or judgment.
Mark was just a callow youth of 16 when he arrived in Paris. 马克到巴黎的时候还是个不谙世事的16岁少年。