Crossword Genius

A number fancy gathering in French square (4,2,5-4)

Ross

I believe the answer is:

when im sixty-four

I'm a little stuck... Click here to teach me more about this clue!

'square' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'a number fancy gathering in french' is the wordplay.
I cannot really understand how this works, but
'number' could be 'sixty' (sixty is a kind of whole number) and 'sixty' is found in the answer.
'french' could be 'f' and 'f' is located in the answer.
This explanation may well be incorrect...

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