Castro stepped down as president following a near-fatal illness in 2006, and his successor, younger brother Raul, has said that his current term ending in 2018 will be his last, ostensibly ending nearly six decades of rule by the brothers.
Openly acknowledging to Cubans that change was inevitable, Raul Castro in February named Miguel Diaz-Canel, 53, as his deputy and heir apparent.
"You never talked about it until Raul said it recently. It was like something taboo," Rey Nunez, a 42-year-old driver, said of generational leadership change. "But I think the institutions in this country are solid for whatever comes afterward."
Fidel Castro has made only a couple of public appearances this year, and last month he skipped celebrations marking the 60th anniversary of the beginning of the Cuban Revolution that were attended by several allied heads of state.
He last was seen pictured with Venezuelan President Nicolas Maduro in late July. In April he paid an emotional visit to a Havana school where he invited staffers to listen to a song eulogizing friend and ally Hugo Chavez, who died of cancer the previous month.
There's no evidence that Castro's health is in immediate danger, though his advancing age is evident in the images published through official channels.
"When you see Fidel now, you realize the calendar is irreversible," said Dayren Silva, a 53-year-old mechanic. "Sometimes I'm very worried that the day he closes his eyes definitively it could be a debacle here, because the situation is so difficult that I don't think Cubans can take it anymore."
Raul Castro is in the middle of social and economic reforms that have expanded independent small-business activity and eased travel restrictions, among other things, though some criticize them as half-measures.
Paul Webster Hare, a lecturer in international relations at Boston University and British ambassador to Cuba from 2001 to 2004, said while it seems clear that Raul Castro is firmly in charge, Fidel's presence acts as a brake on the pace of change.
"I think they're struggling now to find a way of articulating where Cuba will be in five, ten years' time," Hare said, "and I think quite a lot of that is due to Fidel clocking up another year in his innings."
In Miami, where recurring rumors of Castro's purported demise have sparked celebrations in the past, there was neither festivity nor protest.
"I don't know why he's still alive," said Ahmed Medina, 28, who left Cuba when he was 7. His family once owned a successful transportation company but lost it after the 1959 revolution.
"To me, he's dead or dying," Medina said.
Associated Press writers Anne-Marie Garcia in Havana and Christine Armario in Miami contributed to this report.