Mature former pupil promoted wine shop (6)
I believe the answer is:
bodega
'wine shop' is the definition.
(I've seen this before)
'mature former pupil promoted' is the wordplay.
'mature' becomes 'aged' (similar in meaning).
'former pupil' becomes 'OB' (abbreviation for 'Old Boy').
'promoted' says the letters should be written in reverse (going up, in a down clue).
'aged'+'ob'='agedob'
'agedob' written backwards gives 'BODEGA'.
(Other definitions for bodega that I've seen before include "winestore" , "Small shop in Spain selling wine and groceries" , "Shop or cellar in Spain for selling wine" , "Small Spanish grocery and wine store" , "Spanish grocery and wine shop" .)