Naive, like Simon? (6)
I believe the answer is:
callow
This clue is a double definition.
'naive' is the first definition.
('callow' can be a synonym of 'naive')
'like simon?' is the second definition.
(Simon Callow)
(Other definitions for callow that I've seen before include "23 [BRIGHTONIAN] actor" , "Immature and inexperienced, as youth often is" , "Inexperienced or innocent" , "Jejune" , "lacking experience of life" .)