For age it is common and explicit. Senior discounts for instance, and a bit less explicitly, student discounts. It feels better when it is framed as a discount, but it is equivalent to overcharging those who don't get the discount.

For the other categories, it is usually not explicit, but it definitely happens, especially when haggling is involved.

Not the same, in fact the exact opposite.

Student and senior discounts are meant as support/benefits/encouragment, to the poorer and weaker.

The commercial version is about the inverse: skinning every group as much as possible.