I think it is like many interesting questions in science: the answer is probably both
One thing I have learnt since becoming paleo and researching health and aging, is that we are all constantly aging, and it is the degree or pace at which you age which is what is important. Things like chronic insulin, and inflammation are very aging, and it is the buildup of the damage from these that eventually manifests itself as pathology.
Young peoples bodies are much more robust and able to repair the damage that is accumulating, so I think it is their age that let's them get away with it. As you age your repair mechanisms lose their effectiveness which is just a a natural by-product of post evolutionary selection effects, once you are of reproducing age the forces of evolution on you and your ancestors is less strong than they were before.
What is important to remember, that even with Paleo we are still constantly aging, always accumulating damage from metabolism that cannot or will not be repaired. Paleo just allows our body to fully exert its inbuilt mechanisms for dealing with this. This is why I am so big on supplementation; looking at if its "paleo" or not is missing the question. Paleo shouldn't matter if there is solid medical evidence of a compounds effectiveness in delaying aging, like Green Tea for example.
I imagine aging like a long car trip across the country, and your lifestyle dictates the speed at which you drive. Drop high-GI carbs/sugar and the associated blood sugar and insulin rush, and you've just slowed the car down a little. Add in colourful vegetables and berries and you've slown it down a little further. Throw in exercise you slow it down a lot. Get your vitamin D levels up, add some magnesium, fish oil, etc and you've just slowed it down some more.
^^ This is the way I view everything. Everything I do, from 5-10 cups of green tea per day, to a glass of red wine, to high-intensity exercise, to 1mg of lithium at night for my brain, all of these things are culmulative and add together, and I don't think of it as living longer, as getting me from 90 to 100, I see it as slowing my aging down now. That in the next 10 years I will have aged less than the typical 10 years for the typical person. When thought about it like this, I don't see making 100 years old as anything but a choice, the question is if you have the commitment to tweak all the knobs.
I do and so far so good ;)