Old man turned out to be a nut (6)
I believe the answer is:
Here is my best explanation:
'a nut' is the definition.
(almond is a kind of nut)
'old man turned out' is the subsidiary indication.
'turned out' indicates an anagram.
'oldman' anagrammed gives 'almond'.
'to be' is the link.
(Other definitions for almond that I've seen before include "Nut for the old man", "Tree", "Old man (anag)", "Nut often used in cake icing (6).", "Nut-like kernel", "Yellowish brown", "Oval-shaped edible seed", "Fruit kernel of a peach-related tree", "Nutlike seed" and "Nut which provides cake icing".)