Progress made by the old man's son (4)
I believe the answer is:
pass
'progress' is the definition.
(passing is a kind of progressing)
'by the old man's son' is the wordplay.
'by' is a charade indicator (letters next to each other).
'the old man's' becomes 'pas' ('pa' can be a synonym of 'old man'**).
'son' becomes 's'.
'pas'+'s' is 'PASS'.
'made' is the link.
(Other definitions for pass that I've seen before include "Transfer" , "failure in quiz" , "Decline to answer" , "Ratify for saps" , "acceptable exam result" .)