From the comments, Jon offers this take on ageist prejudice…
Regardless of your political views, perpetuating ageist thinking is a disservice to our elders and society in general. Of greater concern than the “McCain-is-old-bashing” going on late night TV shows, is how ageist views also crop-up in “serious” discussions about the election or candidate qualifications, but in more subtle ways.
The presumption seems to be that the chronological age of a candidate (such as Senator McCain or Ralph Nader) in and of itself creates a “negative” hurdle that the candidate must explain away. But where are the questions about whether or how the chronological age of these candidates could be a positive characteristic in relation to carrying out the duties and responsibilities of the President of the United States?
Even it we can’t stamp out ageist thinking in the short term, the debate needs to be expanded to take in to account the positive and developmental aspects of aging as well.