Media group pocketing no returns for ages (5)
I believe the answer is:
yonks
'for ages' is the definition.
(I've seen this before)
'media group pocketing no returns' is the wordplay.
'media group' becomes 'Sky' (broadcasting company).
'pocketing' indicates putting letters inside (pocket can mean to steal or take possession of).
'returns' shows that the letters should be reversed in order.
'sky' placed around 'no' is 'sknoy'.
'sknoy' in reverse letter order is 'YONKS'.
(Other definitions for yonks that I've seen before include "eternity it seems!" , "An age" , "Slang for a long time, ages" , "Long time (informal)" , "Donkey's years!" .)