Youth shy to admit blunder (9)
I believe the answer is:
stripling
'youth' is the definition.
(I've seen this before)
'shy to admit blunder' is the wordplay.
'shy' becomes 'sling' (I've seen this in other clues).
'to admit' is an insertion indicator.
'blunder' becomes 'trip' (trip is a kind of blunder**).
'sling' enclosing 'trip' is 'STRIPLING'.
(Other definitions for stripling that I've seen before include "Young man" , "Youth" , "Young 'un" , "Young boy" , "Lad" .)