If we look at Frankenstein, what do we have? We have a creation abandoned by his creator, thrown into a cruel world naked and afraid. He is ugly and terrifying and society despises him. He is lonely and full of resentment, anger, and sadness. If we look at A Very Old Man with Enormous Wings, we have a mysterious creature of unknown origin that society flocks to out of curiosity and expectation. He too, however, is alone and must harbor feelings of resentment as people treat him like a circus act. However, even when the actual circus (a freak show, actually) rolls into town, he is soon forgotten by the public and must feel even more alone as he spends years in solitude until finally spreading his wings and flying away.
When we look at both stories together, we have two unique and supernatural beings who are lonely and are alienated by society. If the monster from Frankenstein and the winged man from A Very Old Man with Enormous Wings sat down together (assuming they could understand each other) they would find many things in common. They both shared intense loneliness in their lives of solitude and were both treated harshly by society, the creature being deemed an evil and murderous abomination, and the winged man a side-show attraction, painting society as a cruel entity in both stories. But they'd also find that they both did eventually "spread their wings". In the case of the winged-man, he flew off into the horizon leaving behind him his estranged life as a forgotten attraction. In the case of Frankenstein's monster, although a bit more malicious, he too set out on his own as he sought vengeance against the creator who wronged him, Victor Frankenstein, and eventually fled to the Arctic with his creator in pursuit.
So there are some definite similarities here. Both characters, the monster and the winged man, are treated wrongfully by a harsh society that seems to lack any compassion, and they both must face this society alone. One could assume that both authors here are making a statement about society and its cruel tendencies towards mysterious, different, or unfamiliar things and people. Both characters also suffer from lives of solitude, but eventually take flight in their own way.
Although these two works were written in quite different periods, Mary Shelley's novel Frankenstein and Gabriel Garcia Marquez's short story "A Very Old Man with Enormous Wings" have in common that they introduce extraordinary beings into ordinary scenes and use ordinary people's reactions to them as a way of illustrating ethical points.
In the case of Frankenstein's monster, we have an essentially innocent creature abandoned by its creator. It is a sort of tabula rasa (blank slate), acquiring moral character and knowledge from its surroundings. As the monster observes the cottagers, it imitates them and acts in a kind and generous fashion, but when it is rejected and treated with disgust, it becomes evil. In this way it acts as a litmus test or ethical mirror for humanity. The monster also reveals the hypocrisy of Frankenstein in applying ethical standards inconsistently, saying:
“Listen to me, Frankenstein. You accuse me of murder; and yet you would, with a satisfied conscience, destroy your own creature. Oh, praise the eternal justice of man!”
The old man of Marquez's story is a mysterious figure, perhaps angelic in nature. He serves as a test of the charity of the village. The couple at whose house he arrives lock him in a chicken coop. Even though they become rich by displaying him, they do not share their wealth with him, but treat him almost as an animal. The priest, rather than seeing the winged man as something marvelous, or even, at a minimum, insisting that he be treated with Christian charity, simply writes a letter to his superiors and takes no action. By the end of the story, the man, like the monster in Shelley's novel, departs.
In both cases, the insertion of a strange, quasi-supernatural figure into ordinary society acts as a test of the moral fabric of the societies, and one that both societies fail. Both authors seem to be making the point that how we treat people who are different, outcast, or unfortunate (hideously ugly, aged and feeble) is a test of our own character.