Old neon light flickering, one of a set (4,2,3,5)

I believe the answer is:

long in the tooth

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'old' is the definition.
(I've seen this before)

'neon light flickering one of a set' is the wordplay.
'flickering' indicates anagramming the letters (flickering is a type of quick movement).
'one of a set' becomes 'tooth' (I can't justify this - if you can you should give a lot more credence to this answer).
'neon'+'light'='neonlight'
'neonlight' is an anagram of 'longinthe'.
'longinthe'+'tooth'='LONG IN THE TOOTH'

Can you help me to learn more?

(Other definitions for long in the tooth that I've seen before include "Been around" , "over the hill?" , "like smilodon?" , "Was Dracula so" , "aged" .)

I've seen this clue in The Telegraph.

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