Youth in the quarter for Valentine's Day? (10)

I believe the answer is:

fourteenth

'valentine's day?' is the definition.
(14th February)

'youth in the quarter' is the wordplay.
'youth' becomes 'teen' (I've seen this before).
'in' indicates putting letters inside.
'the quarter' becomes 'fourth' ('fourth' can be a synonym of 'quarter').
'teen' put within 'fourth' is 'FOURTEENTH'.

'for' is the link.

I've seen this clue in The Times.

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