Hi, welcome to health care magic
As you stated genetics play a major role in determining a person's final height. Other important factors would be inadequate diet, severe or frequent illness, certain medications and inactivity.Genetics is however the most important.
Most males stop growing by age 16, rarely growth can occur up to mid 20's.
In childhood, if a child is not noted to be growing appropiately and it is thought to be related to a deficiency in growth hormone
then this is administered to induce growth.
Some persons recommended the following: good posture, avoiding the use of alcohol or drugs that may limit height, eating a healthy diet with appropiate amounts of vitamin D and calcium, getting plenty of rest.
I am not sure of the content of the increment tonic and cannot state whether there are any harmful effects, it would be best to take it to your doctor or a pharmacist for definate information
I hope this is helpful to you