How Old Were Mary-Kate And Ashley Olsen When They First Starred On Full House?

Twins Mary-Kate and Ashley Olsen were a mere 9 months old when they made their "Full House" debut back in 1987, but they were only 6 months old when they were first chosen for the part among nine other sets of twins (via Screen Rant).

Twins playing one child character was not unusual then and still isn't today, as of this writing. According to California child labor laws, children between the ages of 2 and 6 can only work for three hours a day, while children under the age of 2 can only work for two hours a day. Using twins to play one character doubles a show's opportunity to feature that young character on screen.

During their time on "Full House," the two little girls became household names as ABC saw Michelle's broad popularity and used Mary-Kate and Ashley together for publicity. They were 8 years old when their run on the sitcom ended, and they had a slew of projects lined up after they took their final bows, eventually starring in 15 movies together over the next few years, according to Screen Rant. Some were made for TV, and some went straight to video, but Mary-Kate and Ashley were already learning to become the shrewd businesswomen they are today.