How old is the adult Michael Myers in the first installment of the series?
In the first installment of the "Halloween" series, which was released in 1978, Michael Myers is 21 years old when he escapes from the mental institution. He was institutionalized at a young age after committing the murder of his sister when he was just 6 years old. He spends 15 years in the mental institution before escaping and returning to his hometown of Haddonfield to continue his killing spree. The events of the film take place on Halloween night when Michael Myers targets Laurie Strode and her friends.