The most common and most likely answer to this crossword clue is the 5 letter word COKES
C
O
K
E
S
Buddy explains!
The straight part
We know that "old fool" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old fool = cokes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COKES mean?
COKES noun- Cola-based soft drink.
- A bottle, glass or can of a cola-based soft drink.
- Any soft drink, regardless of type.
- To produce coke from coal.
- To turn into coke.
- To add deleterious carbon deposits as a byproduct of combustion.
- A simpleton; a dupe.