The riddle "What do you call an old snowman?" is a play on words that is meant to be a bit of a pun.
The answer to the riddle is "Water." The reason for this is that as snow ages and melts, it turns into water. The riddle is a reference to the fact that snowmen are made of snow, and as the snow melts, it turns into water.
The riddle is meant to be a bit of a play on words and is not meant to be taken too seriously. It is a clever way to make a comparison between the snowman and water, in the sense that both are related and one turns into the other. It is also a good example of a riddle that relies on a pun for its humor and cleverness.