Oleff was born in Chicago, Illinois, to Doug and Jennifer Oleff, living there for the first seven years of his life. He then moved to Los Angeles with his parents and began acting. Some of his earliest acting roles include being in a commercial for Coldwell Banker, Guardians of the Galaxy, and reprised the role in the 2017 sequel. Oleff later joined the cast of It, portraying Stanley Uris, one of the seven members of the Loser's Club. Coincidentally, Sophia Lillis, who plays Sydney in this series, also starred in It as Beverly Marsh.
- "Dear Diary..."
- "The Master of One F**k"
- "The Party's Over"
- "Stan by Me"
- "Another Day in Paradise"
- "Like Father, Like Daughter"
- "Deepest, Darkest Secret"
- He has an older brother named Eli.
- His parents' names are Jennifer and Doug.
- His mom is an artist.
- He is Jewish.
- Both of his parents opened up and operated a chain of preschools in the Chicago area before they all moved to the Los Angeles/ Hollywood area.
- He really likes video games, particularly Nintendo ones.
- He occasionally plays the piano.
- He is part German.
- He claims that his hair got curly because he started using some sort of hair conditioner or shampoo that somehow made it like that. It also used to be much more blonde than darker and brownish/blackish.
- at the