Large room containing aged bag (7)
I believe the answer is:
holdall
'bag' is the definition.
(I know that holdall is a type of bag)
'large room containing aged' is the wordplay.
'large room' becomes 'hall' (a hall is a large room).
'containing' means one lot of letters goes inside another.
'aged' becomes 'old' (similar in meaning).
'hall' going around 'old' is 'HOLDALL'.
(Other definitions for holdall that I've seen before include "Large strong bag with handles or shoulder strap" , "Big bag" , "Bag (contents unlimited?)" , "Handled bag" , "retainer" .)