Is life not worth living after age 80?

Someone said this to me and my father-in-law recently and they are a middle-aged person (maybe late 40s) told him that they wouldn't want to live past the age of 80. My dad is in his mid-70s, and still working full time at a job he loves and would love to be in the same field He'll be happy to pursue at least part time as long as he is able to -- think past 100, if he is lucky!

I could tell his feelings were really hurt by this person's expressed view, and I feel it is ageism. I was too stunned to reply at the time, but now wonder what I should have said? Nothing snarky.
Is life not worth living after age 80?
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