I'll explain the reasoning for why companies are reluctant to hire old people:

You can teach things to an unexperienced person, but you cannot unteach an experienced person. What experience an older person has greatly varies, and this experience could be very useful or useless, depending on what the person has done in life.

Unfortunately there is one experience/wisdom which almost all people learn with age, and that is being a knave. Just as our bodies and our minds generally deteriorate with age, so does the soul and the moral fibre - unfortunately. People seem to think that they have to fight the younger generations with deceit and manipulation. And employers aren't too keen to deal with such persons.

But things might also be changing. The people aging right now are of a higher quality than the current generation of old.

Also, many times your best employees will be old people. But they're harder to find.