The KGH method of height prediction acknowledges the role that nutrition plays in your final height. Since there is no simple way of measuring how well you have been eating, the formula uses your current age, height, and weight to make an estimate. It can be off because it does not directly factor in how far you have currently developed. Instead, it uses your age as a rough estimate.
I added an option to replace your age with your Tanner Development Stage number. Since this has not been tested with a study, it should be treated as experimental. However, I believe it will give a better estimate than using your age as an estimate of how far you have developed.