Envious of the young? (5)
I believe the answer is:
green
I believe this clue is a double definition.
'envious' is the first definition.
(thesaurus)
'the young?' is the second definition.
(green can mean young or inexperienced)
'of' is the link.
(Other definitions for green that I've seen before include "member of political party" , ""Go" signal" , "Permission to proceed" , "Like lettuce" , "Lincoln's colour?" .)