What types of societies rid themselves of their elderly?

Nomadic and societies living in marginal or fluctuating environments

The Vikings did, because a lot of them didn't have enough food because Scandinavia at the time was such a harsh environment, that a lot of elders (Except the wise of course) Had to jump off a cliff.

Another name for Viking societies would also be Nordic/Nomadic.

The dots on the scatter plot are all going up