A very old bounder, old fruit! (7)
I believe the answer is:
avocado
'fruit' is the definition.
(avocado is a kind of fruit)
'a very old bounder old' is the wordplay.
'a very' becomes 'av' (I've seen this in other clues).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'bounder' becomes 'cad' ('cad' can be a synonym of 'bounder').
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'av'+'o'+'cad'+'o'='AVOCADO'
(Other definitions for avocado that I've seen before include "Pulpy fruit" , "Alligator pear" , "one's stoned?" , "Tropical fruit with a yellow creamy flesh" , "Tropical tree - edible green-skinned fruit" .)