Prance around farm vehicle, very old inside (6)
I believe the answer is:
cavort
'prance around' is the definition.
(I've seen this before)
'farm vehicle very old inside' is the wordplay.
'farm vehicle' becomes 'cart' (I've seen this before).
'very' becomes 'v' (abbreviation).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'inside' is an insertion indicator.
'v'+'o'='vo'
'cart' going around 'vo' is 'CAVORT'.
(Other definitions for cavort that I've seen before include "Frolic joyfully" , "'Lark about, romp (6)'" , "Romp rowdily, frolic" , "Dance around excitedly" , "Gambol, play about" .)