* The old man is the subject.
* eating a supper is the complete predicate.
The complete predicate is everything after the subject that tells us what the subject is doing or being.
Here's how we can identify the simple predicate:
* eating is the verb (action word) within the complete predicate.
* eating a supper is the verb phrase, which includes the verb and its object (a supper).
Therefore, the simple predicate is "eating".