Your pediatrician will be able to best know your child's normal growth pattern. With that in mind, most parents of full term babies can expect their little one to double their birth weight around age six months.
The first thing I would do is to talk this over with the doctor. He can tell by the parents how big the baby will be. He should double his weight by age 2, if he eats the right diet. Don't load him up with carbs and fats.