Michael J. Fox was 23 when shooting began on Back to the Future, in which he played 17-year-old Marty McFly. The movie was a huge box office hit, but it took four years to get a sequel done. Back to the Future II (1989) and Back to the Future III (1990) were filmed back to back and Fox turned 28 while filming the first sequel (pictured above with Christopher Lloyd in Back to the Future II). However, since the films both take place only days after the 1985 film, he was still playing a 17-year-old Marty.