"This question can be rephrased as: "How much variation (difference between individuals) in height is attributable to genetic effects and how much to nutritional effects?" The short answer to this question is that about 60 to 80 percent of the difference in height between individuals is determined by genetic factors, whereas 20 to 40 percent can be attributed to environmental effects, mainly nutrition. This answer is based on estimates of the "heritability" of human height: the proportion of the total variation in height due to genetic factors."
6 feet = 72 inches. 40% of 72 = 28.8. Meaning that environment can make the difference between 6 feet tall and 3'6" tall. This kind of disproves the notion that it's genetic because it's kind of a given as a human being that isn't deformed that your base genetic potential will be 3'6". Which is just true for being a human organism. The part that actually counts towards anything in this case would be environmental. Even if we take the lower end and say it's only 20% environment, using 6ft as a total height, that would be a 14.4 inch difference. More than a foot. The difference between being technically a midget (below 4'10") and being 6ft tall.