Veteran of sort led badly (7)
I believe the answer is:
oldster
'veteran' is the definition.
(thesaurus)
'sort led badly' is the wordplay.
'badly' is an anagram indicator.
'sort'+'led'='sortled'
'sortled' is an anagram of 'OLDSTER'.
'of' acts as a link.
(Other definitions for oldster that I've seen before include "Senior citizen (colloquial)" , "One aged" , "Wrinkly" , "Person getting on" , "Pensioner" .)