Why About a Boy? (6)
I believe the answer is:
reason
'why' is the definition.
(I've seen this in another clue)
'about a boy?' is the wordplay.
'about' becomes 'rea' (I've seen this in other clues).
'a boy?' becomes 'son' ('son' can be a synonym of 'boy').
'rea'+'son'='REASON'
(Other definitions for reason that I've seen before include "Logic; excuse" , "Justification needed" , "Explanation or motive" , "Purpose" , "Justification; sanity" .)