Is Whole Milk Good For Children Between 11-13 Years Old?

I my nephew is 13 years old, but he is very smart and he always is worried about the heart diseases, most of all Arteriosclerosis; and he only wants food in low fat, low satured fat and low cholesterol, low sodium and carbohydrates. I think that it s an excellent habit, creating at that early age; but the situation is that he is growing and developing himself, and he only drinks fat free milk, I told him that don t be worried about that; he takes care about himself, makes exercise, he eats healthy, salads, fruits etc. So what can I do? should I explain him well the situation about this topic? or should I take him with a doctor and he explain to him all these types of things, I will be living with him for 3 weeks, during my sister is out of town, he is 1,60cm tall, and he weights 130lbs. Any suggestions???