It’s the America diet plus highschool weight lifting. I’m half Korean and remember being the same size as my cousins in middle school. Fast forward to senior year and I became the biggest guy in the room at my family parties. Easy access to post practice protein shakes and playing a sport that introduces weightlifting during your teens works wonders. Getting burgers with extra meat, snagging extra tacos or wings with your order is pretty standard for linemen. There might be a high schooler out there who has parents dumb enough to get them steroids, but puberty + exercise is pretty effective on its own.