Our mom lived in her later years in a military retirement community in Washington, D.C., and during my visits, we would cover all kinds of topics, ranging from family news to dissecting current events.

I sat on one Victorian easy-chair, and she was in another across from me. (Her hearing was good, but lip reading helped.) During one visit when she was 90 years old (she died at age 94), she abruptly changed subjects.

"Where are you going to be buried?" she asked. Looking at the startled look on my face, she quickly added: "You didn't see that coming, did you?"

No, I hadn't. Her question led to a long discussion. We don't have a family plot, she said. Her grave would be with my late father's in Arlington National Cemetery. It would be unfair to leave the decision to my children, she advised, so come up with a plan, let them know I wanted to be cremated, and give them instructions about where my remains should go. She was right.

I bring up the burial question because it's only one of the many complex decisions that people need to address during their retirement years. A far from comprehensive list includes: Where are you going to live? Will you continue to earn an income, perhaps with part-time work? How will you turn savings into income? How best to nurture family relations and strengthen community connections? What is your purpose at this stage of life? These aren't easy questions to deal with, especially considering the inescapable uncertainty about future health and life expectancy.

In sharp contrast, retirement isn't complicated for younger adults. Retirement is an abstraction.

"Like, retirement? It's seriously like asking someone: So have you given a thought to your burial plot? Cremation or burial, what have you decided? Like, I'm 22," said Moshe Milevsky, professor of finance at York University in Canada on the Rebuilding Retirement podcast. "Like, this idea of retirement, come on."

Younger adults are wrestling with their own set of complex life decisions, including finding a career, deciding where to live and perhaps starting a family. For them, Milevsky observed, the realistic action to take when it comes to retirement is to simply focus on investing regularly in a retirement savings plan, stick with low-cost investments and diversify. That's it, for now. Time is on your side.

(And yes, at my stage in life and thanks to Mom, I've come up with a burial plan.)

Chris Farrell is senior economics contributor, "Marketplace"; and a commentator for Minnesota Public Radio.