Force Tory out, not getting any younger (5)

I believe the answer is:

forty

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'not getting any younger' is the definition.
I can't judge whether this definition defines the answer.

'force tory out' is the wordplay.
'force' becomes 'f' (abbreviation in physics e.g. f=ma).
'out' indicates an anagram (out can mean wrong or inaccurate).
'tory' with letters rearranged gives 'orty'.
'f'+'orty'='FORTY'

Can you help me to learn more?

(Other definitions for forty that I've seen before include "Kip" , "Two-score" , "Two score" , "-- winks, a short sleep" , "When life begins" .)

I've seen this clue in The Independent.

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