I mean no offense to any older actors when I say this, but...
At a certain point age becomes a liability if they fall over and break a hip while doing a scene. The frailness of their older bodies is a very real thing and complicates a movie shoot.
That doesn't mean Hollywood should shy away from hiring them, but it means I can understand why Hollywood is hesitant to.
Jamie Lee Curtis is 66, only ten years younger than my own mother, and my mother is so frail it scares me sometimes. Little things take so long to heal. She twisted her knee a small amount in the grass almost two weeks ago and its still a bit swollen.
Ageism is real, but so is elderly frailty and fragility.