In Politics, How Old is Too Old?

According to researchers in Paris, France, the belief that mental decline doesn't start before age 60 is not correct. In reality, cognitive ability--memory, reasoning, and comprehension--begins to go south at age 45. So, what does this mean for America? In a country where 100 million citizens are over 50, and 35 million are older than 65, this could not be good news. And look at our politicians, our leaders: a vast majority of them are over 50, and many into their 60s and 70s. The Speaker of the House just turned 80, our president is 73, and the two men running for his job are pushing 80. Don't these people know when to quit?  And, should people this old be given so much power?