"Put simply, we are having fewer children and living longer," says Michelle Gunn, an Australian journalist and social-affairs writer. Our time is undeniably the age of longevity.

At the turn of the century two and a half years ago, one in every 10 people worldwide was age 60 or older. Demographers estimate the ratio will increase to one in five by 2050 and to one in three by 2150.

Among those age 60 and above worldwide, two in five are over 65 and one in 10 is older than 80. In Japan, however, the graying of the population is far more advanced.