Old hand but never at cooking! (7)
I believe the answer is:
veteran
'old hand' is the definition.
(synonyms)
'never at cooking' is the wordplay.
'cooking' is an anagram indicator (cook can mean to falsify or distort).
'never'+'at'='neverat'
'neverat' anagrammed gives 'VETERAN'.
'but' is the link.
(Other definitions for veteran that I've seen before include "One long experienced" , "One with lengthy experience in service" , "Old hand, ex-service person" , "Old soldier's" , "Describing a pre-1905 car (or pre-1919 at a pinch?)" .)