Older boys on diet badly brought up (9)
I believe the answer is:
mentioned
'brought up' is the definition.
('mention' can be a synonym of 'bring up')
'older boys on diet badly' is the wordplay.
'older boys' becomes 'men' (I can't explain this - if you can you should believe this answer much more).
'badly' indicates anagramming the letters (letters in the wrong order).
'on'+'diet'='ondiet'
'ondiet' with letters rearranged gives 'tioned'.
'men'+'tioned'='MENTIONED'
Can you help me to learn more?
(Other definitions for mentioned that I've seen before include "Brought up" , "Made reference to" .)