Looking at 22 revolutions from 1982 through 2012, the average age of overthrown dictators was 69. For comparison, it’s 55 for all European leaders, and 62 for African leaders. The list:
2012: Central African Republic, François Bozizé, age 66
2011: Yemen, Ali Abdullah Saleh, age 70
2011: Libya, Muammar Gaddafi, age 69
2011: Egypt, Hosni Mubarak, age 83
2011: Tunisia, Zine El Abidine Ben Ali, age 74
2010: Kyrgyzstan, Kurmanbek Bakiyev, age 60
2005: Kyrgyzstan, Askar Akayev, age 60
2003: Georgia, Eduard Shevardnadze, age 75
2001: Phillipines, Joseph Estrada, age 65
2000: Yugoslavia, Slobodan Milošević, age 59
1998: Indonesia, Suharto, age 77
1992: Ethiopia, Mengistu Haile Mariam, age 55
1992: Albania, Ramiz Alia, age 66
1991: Soviet Union, Mikhail Gorbachev, age 60
1989: Poland, Wojciech Jaruzelski, age 67
1989: Hungary, János Kádár, age 77
1989: East Germany, Erich Honecker, age 76
1989: Bulgaria, Todor Zhivkov, age 77
1989: Czechoslovakia, Miloš Jakeš, age 66
1989: Romania, Nicolae Ceaușescu, age 71
1986: Phillippines, Ferdinand Marcos, age 69
1982: Bangladesh, Abdus Sattar, age 76
Criteria: A revolution must involuntarily and successfully remove a non-democratic leader from power through violence, mass protest or other extra-normal means (elections do not count). Age is at time of revolution.
The Rationalist Conspiracy 
Hypothesis: it usually takes a long time for a country’s people to become sufficiently fed up with a dictator to rise up. By the time that occurs, the dictator has gotten old.
Most people don’t mind being enslaved, and giving an unduly large portion of what they earn to those who haven’t earned it. Most humans are born with slave mentality, because being someone’s chattel was a good way to get them to value you, and not kill you before you had reproduced. This is why all tyrant politicians “focus on the family,” to the detriment of the individual. As science advances, productive companies and individuals are bought off, and this becomes a feature of the technocratic state.
Of course, we could just choose to restore enlightenment values that first corresponded to an increase in the power of the jury, dramatically extending human quality of life, lifespan, productive capacity, and wealth. …But that would require the voters to think, and they don’t like thinking. It hurts their tiny brains.
They’d rather die 20 years early, undergo a painful death (at the hands of AMA-licensed and FDA-approved pre-computational-exponential-curve treatments), and leave nothing to their kids, …than think.