Start making Neil out in AA? (5)
I believe the answer is:
milne
'aa?' is the definition.
(AA Milne)
'start making neil out' is the wordplay.
'start' says to take the initial letters.
'out' indicates an anagram (out can mean wrong or inaccurate).
The first letter of 'making' is 'm'.
'neil' is an anagram of 'ilne'.
'm'+'ilne'='MILNE'
'in' acts as a link.
(Other definitions for milne that I've seen before include "A.A. -, Pooh author" , "Children's author" , "Creator of Eeyore" , "He wrote stories for his son, Christopher Robin" , "AA man" .)