Roaring middle age? (7)

I believe the answer is:

forties

I'm a little stuck... Click here to teach me more about this clue!

'age?' is the definition.
(I have seen 'The age' mean 'forties' so perhaps 'age' could also mean 'forties')

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for forties that I've seen before include "British shipping forecast area" , "See 25 Across" , "The age" .)

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

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