Rather old friends (7,2)

I believe the answer is:

getting on

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'rather old' is the definition.
'getting on' can be an answer for 'old' (thesaurus). I'm not certain of the 'rather' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for getting on that I've seen before include "showing signs of age?" , "Succeeding as a boarder" , "as a boarder > in later years?" , "Elderly; succeeding" , "Enjoying friendly relations" .)

I've seen this clue in the Evening Standard.

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