My sons are 5 feet 8 inches and 5 feet 10 inches tall. Their father is 5 feet 9 inches tall. If height were controlled by a single gene and tall were dominant, then only two heights would be possible, tall and short. Even if height were incompletely dominant, in other words, being heterozygous blended the two other phenotypes, only tall, medium and short would be possible. This obviously isn't right.
Height is under the control of more than one gene, perhaps many.
It depends on how many active alleles you inherit from your parents. Lets say that height is controlled by 3 genes each with 2 alleles. So there are 6 possible active alleles, or alleles that actually contribute to height. Lets say that your father is medium tall or has 4 active alleles and two inactive. Lets say mom is medium and has 3 active and 3 inactive.