too early. his bones and growth plates are still soft. He could actually cause permanent bone damage by lifting heavy weights.
Plus, he's a rapidly growing boy, who probably won't eat enough fo the right foods to bodybuild anyways since his body will tear through calories just to grow normally during puberty.
it would be a lot smarter for him to do calesthenics, pushups, crunches, and just get some physical activity/play some sports for a few more years. By 15, he could safely start real weight training.