Was sluggish old man going outside with light? (7)
I believe the answer is:
dawdled
'was sluggish' is the definition.
(to dawdle is to move slowly or sluggishly)
'old man going outside with light?' is the wordplay.
'old man' becomes 'dad' (both can mean one's father).
'going outside' is an insertion indicator (the word goes on the outside of inserted letters).
'with' becomes 'w' (abbreviation).
'light?' becomes 'led' (abbreviation for light emitting diode).
'dad' enclosing 'w' is 'dawd'.
'dawd'+'led'='DAWDLED'
(Other definitions for dawdled that I've seen before include "Dallied, hung back" , "Wasted time" , "Lagged behind" .)