Writer, old, assuredly keeps in front (9)
I believe the answer is:
cervantes
'writer' is the definition.
(Miguel de Cervantes)
'old assuredly keeps in front' is the wordplay.
'old assuredly' becomes 'certes' (I can't justify this - if you can you should give a lot more credence to this answer).
'keeps in' is an insertion indicator.
'front' becomes 'van' (I've seen this in other clues).
'certes' placed around 'van' is 'CERVANTES'.
Can you help me to learn more?
(Other definitions for cervantes that I've seen before include "Author of the novel 'Don Quixote'" , "Spanish writer" , "Bookmaker" .)