Comment concerning a boy (6)
I believe the answer is:
remark
'comment' is the definition.
(a remark is a spoken comment)
'concerning a boy' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'a boy' becomes 'mark' ().
're'+'mark'='REMARK'
(Other definitions for remark that I've seen before include "Mention - observe" , "Comment or mention" , "Something said; take notice of" , "Comment, observation" , "Say as a comment" .)