Disclosure: I'm now a septuagenarian. Sounds better in Latin.
The odd thing is, I don't feel it. Not a bit. So when I first encountered ageism, I went into denial. Or laughed as though it was a joke.
But it isn't. Ours is one of the few human societies in which the default position for age is disrespect. You have to earn your stripes all over again. You either become invisible, or are too often shrugged off with amused or not-so-amused contempt.