Old people.

I wonder if one reason why old people were treated with so much more respect in earlier times is because technology and culture changed and evolved so slowly that by the time you had become a geezer, you had experienced most all there was to experience in life. Plus, since it was so much easier to die before modern medicine, the difficulty of making it to old age, weeded out the foolish along with the unlucky.

By the time you had a long wizard beard you would wellspring of knowledge and wisdom about living in the world.
Whereas today, the opposite is almost true. The way we live our lives and interact with the world changes so rapidly that by the time one becomes an old person, the world is almost an entirely different place than the one they were born and came of age in. Eventually, one is almost like a child, knowing close to nothing about the basic tools people use every day. Calling someone a 'grandma' or a 'grandpa' means they don't understand something that is entirely familiar to most everyone else.
Of course there are caveats and exceptions and one certainly does gain wisdom with age, they just lose relevance.
Which is unfortunate. Some part of me enjoys the idea of there being a segment of society that has already experienced all there is to experience and thus being a source of wisdom.

Perhaps eventually, when we've figured out everything there is to figure out, societal changes will plateau and we will go back to our former attitude towards old age. Although by then people will probably be living forever. If not physically than in some sort of of computer database.