Hard to understand ordinary old man quite without attraction (6)
I believe the answer is:
opaque
'hard to understand' is the definition.
(I've seen this before)
'ordinary old man quite without attraction' is the wordplay.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'old man' becomes 'pa' (both can mean father).
'without' is a deletion indicator.
'attraction' becomes 'it' ('it' can mean an attractive feature).
'quite' with 'it' taken out is 'que'.
'o'+'pa'+'que'='OPAQUE'
(Other definitions for opaque that I've seen before include "Cloudy, non-transparent" , "Not allowing light to pass through" , "Cloudy, not transparent" , "Incomprehensible, impenetrable" , "Not transparent, difficult to understand" .)