In season 3 of Stranger Things, both the characters and the actors are another year older as they navigate the challenges of growing up and grapple with the unknown forces of the Upside-Down. A full year passed between the first season (November 1983) and second season (November 1984), and the third season takes place in the summer of 1985, around nine months after the events of the second season.
But while only nine months have passed for the characters of Hawkins, it's been over a year between the release of the second and third seasons. The longer that Stranger Things goes on, the greater the age difference between the characters and the actors who play them. As is common in Hollywood, most of the actors were already older than the characters that they portray, and this difference has become more pronounced in season 3. Only one of the actors, Noah Schnapp (who plays Will Byers) is currently the same age as the character he portrays. Because the actors' ages vary more than their characters, the actors' ages have been organized from youngest to oldest.
Since the new season takes place during the summer before they start high school, the younger group of kids ‒ Mike, Will, Dustin, Lucas, Max, and Eleven ‒ should be around 13 or 14 years old, depending on when their birthdays are. This means that Nancy and Jonathan should be around 17 or 18, while Steve and Billy, who are both slightly older, are probably 18 or 19. As the middle schoolers transition to high school and the high schoolers transition into college and adulthood, the Stranger Things kids are growing up before our eyes.
As the Hawkins middle school gang prepares for high school, their actors are already old enough to attend. At 14 years old, Noah Schnapp, who plays Will Byers, is both the youngest Stranger Things kid and the only one who is the same age as his character. Millie Bobby Brown (Eleven) is 15 years old, making her only slightly older than her character. Their co-stars Gaten Matarazzo (whose new Netflix prank show came under fire), who plays Dustin, and Finn Wolfhard, who plays Mike, are both 16 years old. Caleb McLaughlin (Lucas) is the oldest of the four boys at 17. Sadie Sink, who is returning to play "Mad" Max in season 3, is also 17 years old.
The older group of Stranger Things kids are played by adult actors who have greater age differences with their characters. While Nancy is around 18 years old, actress Natalia Dyer is 22 years old. Dacre Montgomery, who plays the menacing bully Billy, is around five years older than his character at the age of 24. Finally, both Nancy's love interests, Jonathan Byers and Steve Harrington, are played by older actors: Charlie Heaton is 25, and Joe Keery is 27.
The trailers have introduced audiences to two other characters: Heather, who is a lifeguard with Billy, and Robin, who works at the mall ice cream store with Steve. The exact ages of their characters are not known, but Francesca Reale (Heather) is 24, while Maya Hawke (Robin) is 20.