One inexperienced guy with no rest at work (9)
I believe the answer is:
youngster
'one inexperienced' is the definition.
I can't judge whether this defines the answer.
'guy with no rest at work' is the wordplay.
'with' says to put letters next to each other.
'at work' indicates anagramming the letters.
'guy'+'no'+'rest'='guynorest'
'guynorest' with letters rearranged gives 'YOUNGSTER'.
Can you help me to learn more?
(Other definitions for youngster that I've seen before include "Person of tender years" , "tyke" , "Kid" , "one of tender years" , "Stripling" .)