"A Very Old Man with Enormous Wings" is said to be "symbolic." What is this symbolism?

This is a great issue to raise in relation to this story.
Your question seems to raise a much larger issue about how we as readers interpret and
assign symbols to objects and characters in our often futile attempts to make meaning of
what we read.

I think one of the joys of this short story
is that it defies interpretation. You need to note how the villagers are often exposed
as foolish and gullible in their beliefs, and also how they try to make sense of the
world. They stick fast to "facts" even though they are clearly ridiculous, such as the
fact that angels eat mothballs, and they jump to impossible conclusions, for example
when some argue that the old man should be proclaimed "mayor of the world." It is almost
as if once they have conceived of an idea they make reality "fit" to support that idea
despite any protestations to the contrary - or until a "better" version of the "truth"
comes along and then the process beings again. Of course, the villagers, although they
can be said to be figures of fun in this sense, contain many characteristics which we
can identify whatever our time or culture - for example the unquestioning belief in
their own wisdom and their stubborn clinging to their own ideas are aspects which we can
all identify.

It is clear though that while there are a few
hints into this story as to the "meaning" or "allegory" there are no conclusive pointers
that give one definitive explanation. We are left, much like the villagers therefore, to
try and make some sort of meaning from these strange and bizarre events. The last laugh
seems to be with Marquez, however, as we prove ourselves to be like the villagers trying
to make sense of this story and coming up with very different and ridiculous answers.
Therefore, if there is a "meaning", it is that there is no "meaning" - it is more about
the process by which we make "meaning" and how we support our
conclusions.

So I am not going to answer your question, as
I think if you do try to summarise the angel's symbolic significance you are falling
into precisely the kind of trap that Marquez wants you to fall into! Just be aware that
Marquez is playing with us as readers and trying to get us to assign symbols in our
quest to make meaning of his confusing short story.