First, a word on definitions: Fairytales can generally be regarded as the published children's stories that are literary adaptations of the adult oral novellas of the folk - properly called folktales (or Märchen using the German term, which folklorists often employ). Your question includes the words "and folklore" - this is a broad term that I think we can discard in this context since with that you would be asking about a wide assortment of legends, ballads, and other aspects of oral tradition. For the purposes here, let's stick with fairytales and their core inspiration, folktales.

That said, with your sort of question it is probably easier to describe than it is to explain. I suppose at the outset, I would say that there are many males who oppose the protagonist. The males often appear as ogres or giants, and there are plenty of ferocious male opponents of the hero or heroine in folktales (and fairytales). Numerically, I suspect there is pretty much a gender balance, but I'm not sure of that, and it would be an interesting question that could be checked statistically to test one's intuitive guess as to the occurrences of opponents and protagonists by gender. That would be the descriptive part.

Explaining why old women are placed in the role of the evil opponent is another matter. /u/roryrhorerton* may be correct in saying that we are better asking a cultural anthropologist or a sociologist for an explanation, but either way I would be suspicious of anyone's explanation for something like this.

There can be little question that we are drawn to the vibrant rosy cheeks of youth and repulsed by the sallow sunken face of age. I know that as I get older, I am pretty much horrified every morning when I look in the mirror to shave. I suspect that this is something deep within the psyche of humanity rather than something that is culturally or historically determined. We may be attracted to youth and health especially when it comes to any deeply-rooted instinct to procreate, and we may be repulsed by age because it reminds us of our own mortality. It might be possible to look for broad trends in the perception and characterization of youth/age and of gender in history or comparisons across cultural lines, but that is above my pay grade.

Edit: * I see that this comment was deleted - the redditor directed OP to submit the question to anthropologists or sociologists rather than historians.