Mary-Kate and Ashley Olsen

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Few people become millionaires at the age of 10—but then again, most people don't begin working at infancy. The Olsen twin craze began when Mary-Kate and Ashley were just 9 months old, appearing as baby Michelle on the television show Full House. At just 7 years old, the mini-moguls co-founded Dualstar to market their images to tweens around the world, and at 18, the girls took over the company, estimated to be worth millions.

On October 23, 2008, these world-famous twins discussed their clothing line during their Oprah Show debut.