I've been following some of the discussion at Daily Kos on ageism, so called, as it relates to John McCain. Not everyone is comfortable giving the most powerful office in the world to an old guy who might very well keel over at any minute.
This "ageism" is classed in the same league as sexism and racism. In other words, there is really nothing about a person's personal characteristics that should give us pause before electing him. In this case it's a "he," so that's what I'll say.
Falling down, in a heap, a physical wreck, in shambles, whatever qualities the person has, it would be OK. Because there should be no discrimination, you see, based on physical qualities. He might be nothing more than a shriveled up brain in a petri dish, but as long as we can discern sentience in there somewhere via electrodes applied to his surface, he is a fit candidate for president.
It is the same old story, political correctness run amok. Sexism would be wrong because gender's a quality of people from 0 to 100, and the same with racism, your race in itself is nothing problematic. But truly age can determine several things, depending on the person. Clarity of thought -- and, since I myself am fairly old, I can't think of the others. He's not running for chairman of the Walmart greeters, or president of Phase II of Del Boca Vista, but president. You want someone who is going to be closer to the top of his game.
Age restricts people all the time. You don't see many 75 year old football players, baseball players, or boxers. The airlines don't have many 75 year old pilots. In sports, it's because you have reduced abilities to compete effectively, less stamina, and so on. In flying, it's because of public safety, would be my guess.