Less mature guy Nero corrupted (7)
I believe the answer is:
younger
'less mature' is the definition.
(I've seen this in another clue)
'guy nero corrupted' is the wordplay.
'corrupted' indicates anagramming the letters.
'guy'+'nero'='guynero'
'guynero' is an anagram of 'YOUNGER'.
(Other definitions for younger that I've seen before include "Less mature" , "More youthful" , "More juvenile" , "Less grey" , "More immature" .)