According to the American Medical Association Encyclopedia of Medicine, full adult height is reached at around age 18. Of course other factors such as genetics and nutrition play a role in the growth process.
Humans experience their fastest growth rate during fetal development and early infancy.
For more information on the human growth process, I suggest you consult a human physiology book. Copyright 1998-1999, Room103 group. Don't steal this. All rights reserved. Silica Gel - do not eat.