Most of the Stranger Things kids start around age 12 in Season 1 and are about 14–15 by Season 4, while the older teens are in the 15–19 range and the main adults are in their early 40s during the show’s timeline.

Main kid group

• Eleven (Jane Hopper) is about 12 in Season 1 and roughly 14–15 by Season 4, with an in‑universe birth year of 1971.

• Mike Wheeler is 12 in Season 1 and about 15 in Season 4; his birthday is given as April 7, 1971, in tie‑in material.

• Will Byers is around 12 in Season 1 and about 15 by Season 4, with a March 1971 birthday making him one of the oldest in the core friend group.

• Dustin Henderson is 12 in Season 1 and about 14–15 in Season 4, also born in 1971 in the canon timeline.

• Lucas Sinclair is 12 in Season 1 and around 14 in Season 4, starting high school with the rest of the Party.

• Max Mayfield joins in Season 2 at about 13 and is around 14–15 in Season 4.

Teens and older kids

• Nancy Wheeler is about 15–16 in Season 1 and roughly 18–19 in Season 4, born in 1967.

• Jonathan Byers is about 16 in Season 1 and around 18–19 in Season 4, also with a 1967 birth year listed.

• Steve Harrington is about 17 in Season 1 and around 19 by Season 4, with a 1966 birth year in timeline breakdowns.

• Robin Buckley is introduced in Season 3 at about 17 and is around 18 in Season 4, with a listed birthday in 1968.

• Erica Sinclair is about 9 in Season 2, 10 in Season 3, and around 11 in Season 4.

Adult characters

• Joyce Byers and Jim Hopper are both in their early 40s when the series starts (around 41 in Season 1) and mid‑40s by Season 4, based on information from stage and timeline sources that place their birth around 1942.

These ages are in‑universe estimates compiled from the show, official tie‑ins, and fan‑curated timelines, so some characters have approximate ranges rather than exact birthdays.