Old man and young woman twirling throughout (6)
I believe the answer is:
passim
'throughout' is the definition.
(synonyms)
'old man and young woman twirling' is the wordplay.
'old man' becomes 'pa' (both can mean someone's father).
'and' says to put letters next to each other.
'young woman' becomes 'miss' (title for a young woman).
'twirling' says the letters should be written backwards.
'miss' reversed gives 'ssim'.
'pa'+'ssim'='PASSIM'
(Other definitions for passim that I've seen before include "(Of references) at various places through the text" , "At many points in book" , "(Lit.) throughout, everywhere" , "Throughout (a piece of writing) - frequently cited" .)