Drinker of cool old whiskey to start with (4)
I believe the answer is:
wino
'drinker' is the definition.
(I know that wino is a type of drinker)
'cool old whiskey to start with' is the wordplay.
'cool' becomes 'in' ('in' can mean fashionable or cool).
'old' becomes 'o' (abbreviation).
'whiskey' becomes 'W' (phonetic alphabet: alpha, bravo, charlie etc.).
'to start with' says to put letters next to each other.
'in'+'o'='ino'
'ino' put after 'w' is 'WINO'.
'of' acts as a link.
(Other definitions for wino that I've seen before include "Down-and-out drunkard" , "Big drinker" , "Toper" , "one given to bibulousness" , "Alcoholic" .)