Cuba's demographics are changing because of universal health care, women's rights, emigration, and low birth rates.
Since taking power, in 1959, his birthdays have been marked by mass celebrations in Communist-run Cuba and garnered an outpouring of greetings from across the globe. Each year also added another notch in power, until Mr. Castro became the world's longest-serving leader (a title he still holds, even though his brother is now the chief of staff).
On his 65th birthday, Castro received wishes from thousands of athletes participating in the Pan-American Games in Cuba in 1991. At age 77, he was more isolated, amid a mass jailing of critics in 2003 that drew world rebuke, but he was feted at home. In 2006, when he turned 80 and had just ceded power to his younger brother Raul Castro amid health concerns, crowds gathered to celebrate, and remind the globe, that he was still very much part of the political landscape.
But the celebrations that mark Aug. 13 each year also have become a tally of another type in Cuba: the increasing collective age of its population.
Cuba's National Office of Statistics says about 2 million of the island's 11 million inhabitants, or 17 percent, were over 60 years old last year. That's already high compared to Latin America as a whole, where the rate is somewhere north of 9 percent, extrapolating from UN figures from 2000.