Fear as old man’s about to interfere (5)
I believe the answer is:
dread
'fear' is the definition.
(dread is a kind of fear)
'old man's about to interfere' is the wordplay.
'old man' becomes 'dad' (synonyms).
'about' is an insertion indicator.
'to interfere' becomes 're' (I am not sure about this - if you are sure you should believe this answer much more).
'dad' placed around 're' is 'DREAD'.
'as' is the link.
Can you help me to learn more?
(Other definitions for dread that I've seen before include "Fearful expectation" , "Anticipate fearfully" , "Enormous apprehension" , "Be afraid of - anxiety" , "Deep fear" .)