Simon , actor who played the King of Anatolia in 2003 comedy-drama film Bright Young Things (6)
I believe the answer is:
callow
(Other definitions for callow that I've seen before include "Immature and inexperienced, as youth often is" , "Young and inexperienced" , "Immature and inexperienced, like youth" , "lacking experience of life" , "Inexperienced or unsophisticated, as a youth say" .)