Margaret Hamilton is an inspiration, but is she actually still working at age 83? I can't find anything that would indicate she is. For something like the "longest-working programmer" I'd expect them to have been actually "work"-working during that time.

And I think I'd classify Knuth as the slightly different "longest working computer scientist". He's known for his quote "Beware of bugs in the above code; I have only proved it correct, not tried it."

Or perhaps I'd classify him as the somewhat more sycophantic "longest working genius" or "longest working cool guy". Heck, Knuth was uniquely awarded a master's degree for his bachelor's because his work was considered so outstanding, he's an organist and composer, and he's hilarious. I love this quote about him: "If you had an optimization function that was in some way a combination of warmth and depth, Don would be it."