There's an absolutely fascinating article in the New Scientist that discusses how the planet is aging and what the consequences of that broad demographic shift might be. To give you an idea:
Of all the people in human history who ever reached the age of 65, half are alive now.
If that wasn't enough to hook you, try this:
. . .we are not producing babies like we used to. In just a generation, world fertility has halved to just 2.6 babies per woman. In most of Europe and much of east Asia, fertility is closer to one child per woman than two, way below long-term replacement levels. The notion that the populations of places such as Brazil and India will go on expanding looks misplaced: in fact, they could soon be contracting.
And, if your curiosity about the aging planet isn't satiated by the New Scientist piece, you might also check out our Spring 2008 Stanford Medicine magazine. The entire magazine was a special report on aging.