There’s nothing in turning fifty (3)
I believe the answer is:
nil
'there's nothing' is the definition.
(I've seen this before)
'in turning fifty' is the wordplay.
'turning' shows that the letters should be reversed in order.
'fifty' becomes 'l' ('L' can be a synonym of 'fifty').
'in' backwards is 'ni'.
'ni'+'l'='NIL'
(Other definitions for nil that I've seen before include "Don't despair - . . . desperandum" , "0" , "You get nothing" , "There's nothing left" , "Nothing, no value" .)