Money worries, as might be expected, are more pervasive among younger people — 57 percent of boomers say they feel financially unprepared for such an extended lifespan, while 79 percent of GenXers say the same thing. But despite the financial problems they already face, millennials are a shade more optimistic than GenXers about how they'll survive financially during all those extra years, with 74 percent reporting that they feel financially unready.

Related: Retirement readiness: Slow progress

When it comes right down to it, 45 percent said that "uncertainty" most closely described their feelings about the future. And 51 percent, viewing the notion of "having enough money to last my whole life" found that it could be a very big problem in light of their potential to live to age 100.

Hindsight kicked in, too, at the notion that their lives could be so long; 32 percent regret the major choices they made in their lives, such as when/where they went to school, the profession they chose, and when/where they worked. And 93 percent agreed that people will need to be more thoughtful about how they plan for longer lives.

But when respondents were asked to finish the sentence, "following your dreams is all well and good, but you need to have …," the top two barriers chosen were "enough money" (57 percent) and "a good financial plan" (50 percent). The biggest regret reported (or potential future regret for millennials) was not saving more money (52 percent); that ranked above not traveling more (38 percent) and not spending more time with their kids (32 percent).