Because of the spare, simple style of Hemingway's writing, the best examples of hyperbole are found in the dialogue. Manolin, the young boy, frequently refers to people and things as "the best," or "the greatest," regardless of empirical evidence or proof. It is more important to Manolin, because of his youth, to have unattainable greatness to look up to, and to aspire to, than to look at facts and accept that many things are good, but not great.
"Who is the greatest manager, really, Luque or Mike Gonzalez?"
"I think they are equal."
"And the best fisherman is you."
"No. I know others better."
"Que Va," the boy said. "There are many good fishermen and some great ones. But there is only you."
(Hemingway, The Old Man and the Sea, Google Books)
As hyperbole, this is an exaggeration of Santiago's skills; he is certainly a very good fisherman, because of his age and his experience, but he is only one man and getting old. In Santiago, however, Manolin sees more than the sum of his experience, but the drive of his soul and his passion for his work. Despite his fishing skills themselves, which may easily be simply "good," Manolin designates him as the ultimate fisherman, the one to whom every other fisherman should look for guidance.