HAVANA -- Cuban President Raul Castro turns 81 on Sunday, another reminder to his countrymen and to the exiles who hate him that time is catching up with the island's aging revolutionaries.
But even with the actuarial inevitabilities looming, there is no indication that Cuba's leadership is moving quickly to prepare any younger possible successors to assume the mantle of Marxism under which the island has been guided for more than a half-century.
Even Castro's April 2011 proposal to impose term limits on everyone in government including himself has yet to be enacted. His retired older brother Fidel is 85. His two top deputies are 81 and 80.
"Time and again they've postponed elevating figures from the next generation to the top levels of leadership," said Philip Peters, a Cuba analyst at the Virginia-based Lexington Institute. "It creates some uncertainty."
Discussion of the Castros' eventual demise crops up year after year in a testament to their staying power. But the march of time has been particularly hard on the brothers recently.
The Castros' oldest sister, Angela, died in February at age 88 following a long illness. In September, the president lost a confidant in Gen. Julio Casas Regueiro, his longtime ally and successor as defense minister.
"Casas' death I think took his breath away, because Casas died instantly and Casas really was his right hand," said Ann Louise Bardach, a Cuba expert and author of "Without Fidel: A Death Foretold in Miami, Havana and Washington."
"He had a heart attack and was gone, and at (75) he was their young spring chicken," Bardach said.
Analysts say Castro has peppered top provincial positions and his Cabinet with new faces, including women and Afro-Cubans, some of them in their 50s.
People such as economic reform czar Marino Murillo, Cabinet Vice President Miguel Diaz-Canel and Havana Communist Party boss Mercedes Lopez Acea wield considerable influence in their posts, but none is an obvious heir-apparent.
Castro is believed to be in good health, with no sign of serious physical infirmity. When Pope Benedict XVI visited the island in March and met with both brothers, Raul seemed by far the most spry and energetic of the three octogenarians.
Castro doesn't appear to have the same drive to push himself physically as did Fidel, who often spoke for hours under the punishing tropical sun before a nearly fatal illness forced him from office in 2006. The younger brother seems happy to let lieutenants handle speechmaking on revolutionary anniversaries and appears reluctant to travel more than absolutely necessary.
But the president still carries a heavy load for a man 15 years beyond Cuba's official retirement age, pushing his country to adopt free-market reforms that even he describes as the last chance to save the island's socialist economy. With Fidel looking his years, and Cuba's top patron, Venezuelan President Hugo Chavez, battling cancer, Raul's health is especially crucial to the country's future.
"Raul Castro is a military man, and like a good military man you expect him to prepare for the time that he leaves his post," said Peters. "He has started a process of fixing the economy that has made it a lot easier for the next generation to carry on ... but on the other front of choosing political leadership, it's not at all clear what's been done or how it's supposed to work."
As with everything involving Cuba and the Castros, opinions vary widely. Many older island residents still voice support for the men, while some younger people vent their frustration.
"I hope Raul lives for another 81 years," said Esteban Gonzalez, a 71-year-old retiree in Havana. "With Raul, the country is on the right track for development."
"There has been a lost generation, and not just one but several," said Marta, a 45-year-old cafeteria worker who declined to give her last name for fear that openly criticizing the government could get her in trouble. "Fifty years have gone by with them always telling us that everything was temporary. Well, for how long?"
In Miami, where many exiles have grown old waiting for a change in leadership on their homeland, the birthday marks another year of disappointment.
"The Castro experiment has lasted half a century but it is exhausted," said Huber Matos, who fought in the revolution but broke with the Castros over their embrace of Marxism and served 20 years in prison as a result. "The Castro leaders are old," said Matos, who himself is 93. " ... In a not too distant time, this is going to end."
Associated Press writers Anne-Marie Garcia and Andrea Rodriguez in Havana contributed to this report.