Other forms: gerontocracies
A gerontocracy is a society governed by old people. You might see a gerontocracy in a tribe where elders are esteemed for the perspective and wisdom they have acquired.
If your grandparents moved into your house and started telling everyone what to do, you might be outraged. Daily Metumucil doses for everyone! No loud music or reading of novels written after the First World War! A good thing then, that we live in a culture that worships youth––we're unlikely to be ruled by a gerontocracy.