I put together these two nice charts before I saw Brandon's comment about how the median age is irrelevant :). Nevertheless, I think it's interesting that the U.S. is aging slower than the rest of the world. By 2050, the U.S. is projected to have a median age only slightly above India.
This is the U.S. median age versus the rest of the world. The difference between the U.S. and the rest of the world is 8.5 years in 2000, and only 3.3 years in 2050. (The U.S. is the aqua line in both of these charts.)
And here is the comparison to China, India, Japan, and Western Europe. Certainly the U.S. future looks a lot different.
What are the implications of this?
This fact is obviously very important for marketers. But it may also mean that the U.S. will have an easier transition to an older society than any of the other major global players (China, India, Japan, Western Europe).
Or, as Brandon says, it may not mean much at all. I've certainly argued in the past that demographics is trumped by growth.
Take a look at this chart, which plots two different scenarios for world income per head versus the projected path of the median age. At 1% growth in per capita income, the economy barely keeps up with the aging of the population. At 2% growth, however, the economy gets way ahead, and the impact of aging won't be so bad.