Tall stature refers to a height at any age above the 97th percentile. Adults who are above the 97th percentile for height are considered very tall. This metric is true for both boys and girls. In India Endocrinologists use the IAP growth chart to determine whether a child is too tall.
A child who is very tall, and having a very tall predicted adult height can be stopped from growing too tall, by a Therapy which can close the growing epiphysis. In boys testosterone supplementation can be given. In girls, estrogen supplementation is given.
The most common reason for tall stature is- both parents being tall. This is called familial tall stature.
Tall stature is usually genetic in nature due to tall parents. However there are conditions where tall stature can indicate an underlying medical problem which needs to be treated separately. GH producing tumors of the pituitary gland can result in gigantism or tall stature. The usual clue in such patients is that the children are excessively tall when compared to the parents height– that is the predicted adult height is much higher than the calculated Tanner height prediction.
Another important cause for tall stature is non-fusion of Epiphysis due to puberty. This occurs in individuals who have not had puberty due to hypogonadotropic hypogonadism. Hypogonadotropic hypogonadism refers to a genetic defect where the hypothalamus and pituitary do not mature and trigger puberty. Since gonadal hormones are responsible for fusion of Epiphysis, prolonged deficiency of these hormones can result in very tall height.