No, some proportion of them would have been dead between 0 and 3 years old (which is what brings down the life expectancy numbers dramatically) but 100 years ago those 50 year olds would still be living to 60, just like they do now.
http://www.infoplease.com/ipa/A0005140.html
A 20 year old can expect to live well into their 70s rather than just reaching 60 (so an expectancy of ~55 years compared to 40 years).
But sure, the gains are mostly from early survival rates.
I do see guys my age in menial jobs, and I believe it's the economy. Companies just fired people. They fired them for various reasons, but technology made it possible. It's result of decling availability of good unions, or any unions--hence no real retirement. A changing workplace. Less jobs.
If anyone should be worried about their economic viability, I believe, young tech workers are high on the list. No unions. Training/work that can be farmed out. Training that can be learned over the Internet--well. I don't want to be an alarmist, but I know too many former Programmers. Too many unemployed/close to homeless Programmers from the 80's and 90's?
I see a trend towards doing well with less employees, and no one cares as long as they get what they want. What's App has a handful of employees? Twitter will never have the amount of employees they had a week ago, even if they do really take off. We are making programming/Web developement easier daily. I'm happy with DRY. I like Bootstrap. What will it be like in another ten years?
I don't have an answer, but I don't forsee a bunch of 50-60 year old employees bagging groceries. I just see the more Homeless. I believe it will get so bad, the rich won't be able to fully enjoy their wealth, unless they beef up entitlement programs? After all, driving your sport's car past homeless can't be fun, and then you have to think about where you can park it? It's kind of like eating a fancy dinner, while the person across the table is starving? And let's not turn into Mexico, where if you have some wealth, you can't leave the house unless you have body guards.
Got off track, but the future does not look rosey. I do think we need to resind some of these treaties that make opening up shop overseas so easy, or at least raise tariffs? I know it's selfish, but the way we are moving is scary.
It's hard to measure quality of life, but if you look at things like housing, people in the US have more households now, with the average dwelling having increased in size (I'm sure McMansions pull up the average, but again, oversized houses aren't evidence of scarcity).