Numerous thoughts:
I read an article in a magazine at the doctor's office a year ago that made a statement I found surprising: It said that 50% of the babies born this year will live to be 100. Obviously, none of us can possibly know whether this is truthful or not, but I'm sure it's about better vaccinations, better medical care, etc. And the article did not address the effects of obesity, diabetes, and the like, which have skyrocketed in the past couple decades.
Anyway, if that's true, people will have to support themselves somehow, and the work force is changing at a scary pace. Automation means that we need fewer people to do the grunt work ... so how will the idiots among us support themselves? People who do manual labor won't be able to do it until they're 100. The most likely idea is that WE will support them.
Even if you're not an idiot, if you're likely to live to 100, you'll need to put away more money than if you're expecting the 80-odd years that is the average today. That extra 20 or so years will make a difference -- inflation, etc.
And, yes, if people are staying in their jobs longer, it does mean that the younger generation can't "get a start". OR it means that with less job security, the "old folks" will get the boot (now that I'm upper 40s, I assure you that discrimination against older workers is real -- I see it clearly) and will be forced into menial labor jobs.
The article referenced in this thread says that 30-80% of the jobs Americans hold today will no longer exist in 10-20 years. First, that's a huge guess -- I mean, just look at the numbers. But it's scary for today's young people. I mean, look at what's already happened: My mom worked in a clerical job in the late 60s; that job no longer exists: her specific job has become a "serve yourself" thing on the internet. Only a few people work in that industry now, and they're just cleaning up the occasional mess. Today machines can replace all the fast food workers, meaning that a restaurant could run with only 2-3 people per shift to oversee things -- so that huge number of unskilled workers could easily find themselves without jobs.