Lost red bats and grey one (7)

I believe the answer is:

oldster

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'grey one' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

'lost red bats' is the wordplay.
'bats' indicates an anagram (slang for mad).
'lost'+'red'='lostred'
'lostred' is an anagram of 'OLDSTER'.

'and' is the link.

Can you help me to learn more?

(Other definitions for oldster that I've seen before include "codger" , "Elderly person" , "One no longer inexperienced" , "Experienced person" , "He's more experienced" .)

I've seen this clue in The Independent.

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