Old man about to get trim (4)
I believe the answer is:
pare
'trim' is the definition.
('pare' can be a synonym of 'trim')
'old man about' is the wordplay.
'old man' becomes 'pa' (both can mean father**).
'about' becomes 're' (regarding).
'pa'+'re'='PARE'
'to get' is the link.
(Other definitions for pare that I've seen before include "Shave or peel" , "Cut down gradually" , "Decrease gradually" , "Remove the skin from" , "Trim by cutting" .)