You might think it is due to high metabolism and anyway you or he don't grow bigger, it is fine to keep eating.
When you eat more, are you taking highly nutritional food from wholesome plant, fruits and vegetables or high processed (junk) food such as, meat, dairy and oily food?
Food can heal.
Food can harm.
Be a wiser consumer.
Food for medicine.
Being healthy is not a goal.
Being Healthy is a way of Life.