(Though let us be clear, the idea of a named disease is a nebulous entity: "Alzheimer's" probably covers at least three distinct conditions, for example, and it's much the same for Parkinson's and many other diseases that were named early and only now are being split out into their various etiologies. Ultimately at the level biotech is moving into now, names for collections of symptoms and similar-looking damage go away in favor of treating specific mechanisms that get you there).
To show just how much of a cost the FDA imposes just by this regulatory aspect, you might look at sarcopenia: it has cost millions of dollars and years to date and will cost millions and years more to lobby the FDA (meaning put dollars into the pockets of lawyers and appointees) to recognize sarcopenia as a condition. Until that happens, there will be no serious commercial research into the numerous potential mechanisms and therapies, because you can't sell the results in the US.
Now multiply that by the thousands of potential named conditions you could carve off the bulk of mechanisms that is called aging. Look at the SENS Foundation research pages for a primer on the underpinnings:
http://sens.org/sens-research/research-themes
So given this ridiculous state of affairs, pretty much par for the course for big government, therapies for aging will never happen in the US for so long as the present regulatory structure exists, and for so long as there is no massive medical tourism and global research and development exchange devoted to circumventing it. That latter community is only just getting started, when considered in the grand scheme of things.
But most people are blind to all of this, and think that the FDA is actually a force for good - because they don't see the opportunity cost and the progress that didn't happen. In fact, the FDA and its equivalents overseas are the biggest obstacle to significant medical progress in this age of revolutionary advances in biotechnology.
http://www.fightaging.org/archives/2012/04/the-fda-is-a-dest...
For more reading on the "is aging a disease" thing, you might look at:
http://www.fightaging.org/archives/2010/05/talking-point-is-...
"Because aging is not viewed as a disease, the whole process of bringing drugs to market can't be applied to drugs that treat aging. This creates a disincentive to pharmaceutical companies to develop drugs to treat it," said Gems.
http://www.fightaging.org/archives/2009/07/sage-crossroads-p...
Why, despite the great range of potential applicable biotechnology, do we not see hundreds of millions of dollars invested in startups attempting to address the aging process? The answer is buried in this New York Times article on Sirtris: "Dr. Westphal and Mr. Sinclair stress that they are not working to 'cure' aging, a condition that, so far at least, is common to all humanity and that most physicians do not consider a disease. 'Curing aging is not an endpoint the federal drug agency would recognize,' Dr. Westphal says dryly. Instead, both men say, they are working to ameliorate the diseases of aging."
...
LARRY MILLER: [When] I was heading aging at Glaxo Smith Kline, the issues that I faced were that I was very interested in developing medications for frailty and weakness in muscle for when people get old because when people get weak they usually stop eating and then they fall and break a hip and end up in the hospital and die potentially, but the regulatory apparatus isn't there yet. Sarcopenia isn’t recognized as an official disease by the FDA, so the pathway to get drugs approved for frailty and to get more people mobile and into society is just not there.