PHOTOS: What it's like to be 72 — the faces (and wisdom) behind the age

((Clockwise from upper left): Light Oriye for NPR; Chiara Negrello for NPR; Rajaâ Khenoussi for NPR; Jjumba Martin for NPR; Debsuddha Banerjee for NPR; Debsuddha Banerjee for NPR; Maíra Erlich for NPR)

The world's population is facing a historic shift: By 2030, one in six people will be age 60 or over.

So every nation will face the rising social, economic and health-care challenges that accompany an aging population. Low- and middle-income countries – the world's fastest growing — will drive the most change: By 2050, these countries will be home to two-thirds of the world's population over age 60.