Old man making climb with little desire (8)
I believe the answer is:
appetite
'desire' is the definition.
(I've seen this before)
'old man making climb with little' is the wordplay.
'old man' becomes 'pa' (both can mean father).
'making climb' is a reversal indicator (in a down clue, letters go up).
'with' says to put letters next to each other.
'little' becomes 'petite' ('petite' can be similar in meaning to 'little'**).
'pa' written backwards gives 'ap'.
'ap'+'petite'='APPETITE'
(Other definitions for appetite that I've seen before include "Desire, relish" , "Physical need for food" , "Natural craving" , "Natural desire to satisfy a need" , "demand" .)