Old enough to have the 'Freedom' of London (transport) (7)

I believe the answer is:

elderly

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'old' is the definition.
(elderly means old or aged)

I cannot understand how the remainder of the clue works.

(Other definitions for elderly that I've seen before include "Mature" , "... or not of tender years" , "Fairly old, past middle age" , "Past middle age, a senior citizen" , "Silver" .)

I've seen this clue in the Evening Standard.

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