[yellowbanana]

it's generalizing rather than looking at the individual characteristics.

If someone cant learn fast and that's an in important requirement to a position don't hire them.

But if the idea is statistically speaking old people don't learn fast so I am going to generalize and conclude I can't hire "old" people，that's bad and also is missing out.

This is the same idea behind racism, sexism, ... Assuming that because on average something is true so an individual coming to you will be judged first on an average of the group you see them in, above their Individual characteristics