Tanners perhaps - they made their fortune some time ago (3,5)

I believe the answer is:

old money

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'tanners perhaps they made their fortune some' is the definition.
I know nothing about this answer so I can't tell whether this works.

'time ago' is the wordplay.
'time' becomes 'old' (old is a kind of time).
'ago' becomes 'money' (I can't justify this - if you can you should believe this answer much more).
'old'+'money'='OLD MONEY'

Can you help me to learn more?

I've seen this clue in The Irish Times.

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