In collectivist societies, ageism doesn't exist. Old people are revered for their wisdom and considered assets to society still. In these nations (which are mostly east Asian, off the top of my head), older people actually end up being in much better shape and still legitimately sharp in mind as well. Old people in this nation and others like it, individualist societies, are practically dismissed and expect to become retards who shit themselves and argue with people over ten cents. They're seen as a burden. They suffer physically and mentally and fulfill the extremely low expectations of their society.
There are huge differences regarding ageism towards youth, but I don't want to become too invested in a thread about classism.