PORT CHARLOTTE, Fla.—Forrest Yeager, a 91-year-old resident of this seaside community, had been counting on his retirement savings to last until he died. The odds are moving against him.

With short-term bank CDs paying less than 1%, the World War II veteran expects his remaining $45,000 stash to yield just a few hundred dollars this year. So, he's digging deeper into his principal to supplement his $1,500 monthly income from Social Security and a small pension.

"It...