The world’s most significant social, political and economic development is its aging population. Little wonder that Europe has declared 2012 the year of active and healthy aging.

Within five years, for the first time in history, the number of adults 65 and older will exceed the number of children younger than 5, the World Health Organization reports. By mid-century, this demographic will outnumber children younger than 14, and more than 2 billion of the people on Earth will be 60 or older.

By 2050, U.N. data show, 33 countries will each have more than 10 million citizens who are 60 and older, including Brazil with 58 million, China with 437 million, India with 324 million, Indonesia with 70 million and the United States with 107 million.

These fast-changing demographic trends are inexorable — which is why the aging global population’s impact on social stability, economic growth and fiscal sustainability should be part of the agenda at next month’s Group of Eight summit.

The challenge is not simply that people live longer — three more decades since the beginning of the 20th century. The world is also coping with stunningly low birth rates. Together, these issues create a new proportion of “young” and “old.” In Britain, Germany, Italy and Japan, roughly 40 percent of the population will be older than 60 by mid-century. Other G-8 members are not far behind. The G-8 summit at Camp David is an ideal place for the United States to take the lead on this issue.

Can it be a coincidence that, under the weight of this demographic transformation, the 20th century’s social contract is coming apart at the seams? With Greece, Ireland, Portugal, Spain and a number of U.S. states facing huge budget challenges, the consequences of applying last century’s economic and social policies to today’s demographic realities are stark. The arithmetic simply does not work. Japan, the world’s “oldest” country, has done the math, and for next month’s annual World Health Assembly, it has put forward a progressive resolution aimed at health reform for non-communicable diseases that are linked to aging, such as Alzheimer’s, cancer, diabetes and cardiovascular disease.

And yet, the agenda for the G-8 summit appears deficient on the topic of how countries can work together to develop policy reforms that would create pathways for healthy, active and productive aging. The stakes are high. We cannot continue to bicker over how to bail out Europe’s southern tier. Without serious policy reforms as the century progresses and the world continues to age, there will be no one left to bail it out.

What’s needed are profound policy changes in health, education and urban living that facilitate an active aging. What if we reimagined and redefined what it means to age? What if, in light of our longer lifespans, “middle age” were 55 to 75? What if we enabled our innovations and technologies to position aging populations to drive economic growth?

What if we redesigned the education process so it accounted for our longer life spans and the changing needs of our workplaces? What if we dedicated basic research-and-development funding to the big diseases of aging, such as Alzheimer’s and cardiovascular disease, and other impairments to active aging, such as vision deterioration and bone frailty? And what if we followed the Global Network of Age-friendly Cities and Communities — that genius invention of the World Health Organization — where communities’ housing, transportation, social services and education were aligned to aging populations, not just because it’s the right thing to do but also because it’s in everyone’s economic and fiscal interests?

If President Obama can be flexible enough to move the G-8 meeting from Chicago to Camp David, he could direct administration officials who are crafting the agenda to add a topic that has such profound and far-reaching effects for our planet. How we organize ourselves, which institutions are relevant and where we spend our funding will be determined by our aging population. Surely that’s worthy of some discussion by the G-8.