Old city to mature the area (7)

I believe the answer is:

acreage

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'the area' is the definition.
(acreage is a kind of area)

'old city to mature' is the wordplay.
'old city' becomes 'acre' (I can't justify this - if you can you should believe this answer much more).
'to mature' becomes 'age' ('age' can be a synonym of 'mature').
'acre'+'age'='ACREAGE'

Can you help me to learn more?

(Other definitions for acreage that I've seen before include "good quantity of land" , "Farm" , "Amount of land" , "Land area" , "Area measure" .)

I've seen this clue in the Sydney Morning Herald.

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