Inexperienced? No, guy's trained (5)
I believe the answer is:
young
'inexperienced?' is the definition.
(thesaurus)
'no guy's trained' is the wordplay.
'trained' is an anagram indicator (to train can mean to grow something into a shape).
'no'+'guy'='noguy'
'noguy' anagrammed gives 'YOUNG'.
(Other definitions for young that I've seen before include "Green" , "Fry" , "Inexperienced" , "Of tender years" , "not getting on yet" .)