A vegan ate a vegan diet for fifty years or more? I rather doubt it. It amazes me how many of these vegans only last a decade or two and were healthy when they began, else they could not have maintained it that long. So no, I'm not going to judge the healthfulness of a vegan diet by whether an elderly person is eating it. For all I know they adopted the diet five or ten years ago, hardly time for it to have affected how they've aged.
Sorry, but we're not five or six different species and I don't believe we all need such radically different diets. There is a wide range of what we can tolerate and there are slightly different dietary approaches depending on one's health status. But we are not a single species comprised of both insectivores-turned-nonobligate-carnivores and herbivores. It doesn't work that way.
Let 'em do what they like but I hardly feel the need to emulate them if I know the diet's wrong, on its face, for my physiology.
Not that I think there is any such thing as a THE Paleo Diet either. There are lots and lots of ways to be Paleo. Mind you, all of them involve animals in the diet. No way around it.
(edit) Actually, I tell you what, the way people change their dietary habits these days, sometimes every ten years or so, I wouldn't look to any elderly modern people to say this diet or that diet is the best. I would rather look to the indigenous with little to no industrial food in their diets because they have much more consistent dietary patterns. Look at some of the African tribes who haven't modernized yet, for instance. They might be wrinkly in the face from sun exposure but they're also wiry and strong. Look at how they've eaten. That's more what I would follow, at least in approximation of macronutrient intake and food types (ruminant, leafy vegetable, etc.).