Let's start today with some numbers, some demographic statistics that I think you'll find surprising.

Here's the first one. Within 10 years, there will likely be more people in the U.S. 65 and older

than there are people 18 and younger. This is a brand new state of affairs, and the rest of the world is

following the same path. Let's call it the elder swell. How can this elder swell be explained?

It's been driven by two big trends, lower fertility, which we talked about in part one of this

series, and a massive increase in

life expectancy, especially over the past century and a quarter. That is thanks to, among other

things, more abundant food, cleaner air and water, less war, and vastly better public health

and medical care, especially the treatment and prevention of

diseases that used to kill so many children. But the real headline of the elders swell is not

just that more people will be living more years, it's that those years are expected to be better.

This is what researchers call health span versus lifespan. Let me give you another set of surprising statistics.

The International Monetary Fund recently conducted a study of older people in 41 countries.

It included both physical and cognitive testing.

The researchers found that, on average, the physical condition of a modern 70-year-old corresponds to that of a 56-year-old in the

year 2000. And a 70-year-old person today has the same cognitive ability as a 53-year-old person

in 2000. Now, much of that gain comes from lower-income countries, which had more

catching up to do.

Still, it is a remarkable gain in health span over just a couple decades.

So, today, on Freakonomics Radio, how can we prepare for the Elderswale?

One of the great achievements of the 20th century is to produce an aging society.

It's so weird we see it so negative. We'll look at whether our infrastructure is ready for the elder swell. One of the great promises that the American

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