Yes not all people are going to be 200lbs of muscle im not and will never be. The kid doesnt want to be skinny. He may be a healthy weight naturally im not disagreeing. But he wants to gain weight. He will if he eats more that's a fact and no matter what his metabolism may be it true. he may need to eat 10,000 calories to be 180lbs were i need 3500. But if he eats it he will.
His diet is what is limiting that the end of the story. If he doest fix that he will never gain the weight he want steroids or not.