Millie Bobby Brown was 12 years old during season 1 of Stranger Things , both in real life and in terms of Eleven’s age in the story.

Millie’s age in season 1

  • Millie Bobby Brown was born on February 19, 2004, and Stranger Things season 1 premiered in 2016, making her 12 at the time.
  • The character Eleven is also written as about 12 years old when we first meet her in season 1.

Quick context for fans

  • Several entertainment outlets note that “Millie and Eleven were both 12 in season 1,” highlighting how closely her real age matched her character then.
  • This is part of why many fans talk about how the young cast has “grown up on screen” from season 1 to the later seasons.

TL;DR: Millie was 12 in season 1.