You're quite right Steve. We've evolved admirably, but we now expect to eat rubbish and live sedentary lives, neither of which are included in the blueprint for our new, long-lived bodies.
Increased life-expectancy is great, but what state are we in to enjoy it eh?
Oddly enough, although the 'Third World' dwellers have had appalling conditions to endure, and their life-expectancy has been much shorter than ours, they seem to me to now be having a better chance. They don't eat junk food, walk everywhere and never over-eat or become obese. Those who survive the very high rate of infant mortality are actually (in my view) in better shape than us in many ways. My very ancient father-in-law (we think he's in his early nineties, but no-one knows when they were born over there!) is quite frail but has most of his teeth, still walks far and wide and can get down on the floor to pray and get up again (I can't do that!) He's never smoked or drunk alcohol, and his diet has been meagre but with no additives, sugar or animal fat. He's far from senile and I reckon at this rate he'll outlive me, if, touch wood, one of the many deadly diseases in W Africa doesn't carry him off.