I guess it depends on what you mean by stress. But one source of stress is the process of decision-making. And we have many more options these days which makes decision-making more stressful.
For a lot of people in the world (and in the past), they grew up knowing pretty much what their role in society is going to be and roughly what they are going to be doing for most of their life. Dad was a farmer or blacksmith? Well, that’s probably you’re going to be. Even if the details contain stressful elements, in the absence of major catastrophes like war, famine, or plague, you can pretty much paint by numbers for most of your life.
Contrast with today’s society – you’ve got a million choices and few chances to get it right. You have to pick the right schools, the right major, the right occupation, the right place to live, the right car, the right partner, and all the time the television is telling you that you could do better – look at all these people in flashier, better paying occupations with hotter wives/husbands.
There’s also the problem that once you’ve experienced a certain standard of living, it truly sucks to lose it. So we spend most of our lives wanting more, afraid to lose what we have now, and vaguely dissatisfied at the same time because there are other things we could be doing if we had made other decisions, were braver, richer, or less encumbered.
Then again, I haven’t lived in terror of a press gang, contracted bubonic plague, or been caught between a mob of angry Huguenot and Catholics, so what do I know from stress?