Michael J. Fox was cast as Marty McFly after the original actor was fired, and as a 23-year-old, he convincingly played a 17-year-old high school student. Christopher Lloyd played the eccentric scientist Doc Brown at two different ages, 35 and 65, while being 46 during production. Lea Thompson, who portrayed Marty's mother, Lorraine, had to look like a 17-year-old and a 47-year-old, even though she was the same age as her costar, Michael J. Fox.

The ages of the cast and characters in Back to the Future are a bit convoluted, given that the movie takes place in two different timelines and some actors play their roles as teenagers and adults. The science action film premiered on July 3, 1985, and depicted a teenager accidentally traveling back in time (to 1955) via a DeLorean time machine that his older scientist friend built. Unfortunately, while there, he accidentally interferes with the timeline and threatens his own existence...