Shaver's gone rusty, unfortunately (9)
I believe the answer is:
youngster
'shaver's' is the definition.
(synonyms)
'gone rusty unfortunately' is the wordplay.
'unfortunately' indicates an anagram (a bad or unfortunate spelling).
'gone'+'rusty'='gonerusty'
'gonerusty' anagrammed gives 'YOUNGSTER'.
(Other definitions for youngster that I've seen before include "Stripling" , "one of tender years" , "One not fully mature" , "Tiddler" , "Rug rat in New York" .)