"What if age is nothing but a mind-set?" asks NYTimes Magazine article
The article begins with a fascinating experiment conducted by Harvard psychology professor Ellen Langer back in 1981. In it, a group of elderly men were brought to a site for a week where they were induced to imagine themselves as they might have been a couple of decades earlier. The result? As Prof. Langer phrased it, the men in the experiment "'put their minds in an earlier time,' and their bodies went along for the ride."
To be sure, some other academics reject the reported results, for a variety of reasons, including the design of the experiment.
Others, I gather, would reject it and other experiments on the grounds "Everyone knows that sort of stuff is impossible.". Prof. Langer responds, "To which I would say, 'There's no discipline that is complete. If current-day physics can't explain these things, maybe there are changes that need to be made in physics,'"
Yes, her work also addresess the issue of placebos (and the opposite: nocebos), and the effect of expectations. I won't get into that here, just encourage you to read the whole article.
Here's the link: NYTimes article. It will also appear in the NYTimes Magazine's paper issue of October 26, 2014