I think the reason why he passed off as 12 is because some 12 year olds do have body hair, are tall, have a deep voice, have facial hair, men's body my brothers had all those when they were 12. They went through early puberty. It runs in our family. So the schools assumed the same of him, went through an early growth spurt, already had his voice changed, got a men's body but hasn't started to develope facial hair and body hair yet.