Lack of experience (7)
I believe the answer is:
naivety
'lack of experience' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for naivety that I've seen before include "State of innocence or simplicity (7)" , "Navy tie? (anag)" , "Quality of impractical innocence" , "Ingenuousness" , "artlessness" .)