Having already grossed more than $10 million in previews, “Backrooms,” the latest feature from A24 and the debut directorial effort of 20-year-old Kane Parson, is already posed to be a box office hit.

Backrooms,” a psychological horror flick opening this weekend, is part of a wave of breakout films from fledgling directors who honed their instincts on YouTube.

Now 20, the viral creator Kane Parsons is releasing “Backrooms,” a feature-length expansion of his web series.

Parsons has gone from YouTube creator to A24’s youngest-ever director A24 Indie horror film Backrooms is poised to become one of this summer's biggest hits upon its May 29 release. Who is the ...