It seems to me that there are a couple of ways that the McCain people could get the Obama people to back off on the age thing. One way is to ask Barack "New Tone" Obama straight out whether he believes that McCain is too old to be president, as his allies are suggesting. If he says "yes," well, there goes the new tone -- along with a good portion of the elder vote (and, unlike the youth vote, it's one that tends to head reliably to the polls). If he says "no," then there's the response each time one of his surrogates tries to play around with words like "confused." If he weasels, well, it's just another opportunity to point out that with Barack, one may be getting a lot of words without getting a lot of substance.
The point is that in a graying society, it's not perhaps the smartest approach to act as though an obviously capable presidential candidate is in his dotage simply because he misspeaks from time to time. After all, old age wouldn't explain Barack's well-documented history of gaffes.
But -- as McCain's people might be well-advised to point out -- perhaps youth and inexperience would.