Repeat concerning young (5)
I believe the answer is:
renew
'repeat' is the definition.
(thesaurus)
'concerning young' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'young' becomes 'new' (similar in meaning).
're'+'new'='RENEW'
(Other definitions for renew that I've seen before include "Extend loan period" , "Replace" , "what regeneration will do" , "Give fresh life to" , "Extend (subscription)" .)