Millennials are about to be surpassed by Generation Z.

Gen Z will comprise 32 percent of the global population of 7.7 billion in 2019, nudging ahead of millennials, who will account for a 31.5 percent share, based on Bloomberg analysis of United Nations data, and using 2000/2001 as the generational split.

People born in 2001 will turn 18 next year, meaning many will enter university, be eligible to vote and, depending on their citizenship, smoke or drink alcohol without breaking the law. Gen Zers have never known a non-digital world and have grown up amid events such as the "war on terror" and Global Recession.

"The key factor that differentiated these two groups, other than their age, was an element of self-awareness versus self-centeredness," according to “Rise of Gen Z: New Challenge for Retailers,” a report by Marcie Merriman, an executive director at...