Young girl with old rope (5)
I believe the answer is:
lasso
'rope' is the definition.
(lassoing is a kind of roping)
'young girl with old' is the wordplay.
'young girl' becomes 'lass' ('lass' can be a synonym of 'young girl').
'with' is a charade indicator (letters next to each other).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'lass'+'o'='LASSO'
(Other definitions for lasso that I've seen before include "A cowboy's looped lariat" , "Cowcatcher" , "Rope for a cowboy" , "Long noosed rope used to catch animals" , "Catch (steers) with a rope" .)