What is the meaning and the appropriateness of Hemingway's The Old Man and the Sea?

The Old Man and the Sea is an allegory, which means it has two levels of meaning: literal and metaphorical.

In the literal sense, it is about an old man who has bad luck fishing, but once he is able to break the curse, he catches an enormous tuna that is stolen from him by sharks.

On the metaphorical level, it is the opposite of the rite-of-passage story: the loss of masculinity as a result of age. The old man, strong and experienced as he may be, loses his greatness and must resign to being old, at the mercy of the young who can provide for him.