"The aetiology of gigantism will clearly depend on the definition. If one uses the term broadly, merely referring to a height two or more standard deviations above an age, gender and Tanner stage matched cohort, then most cases will merely be physiological tallness 3. In contrast, by far the most common cause of pathological gigantism is the presence of growth hormone secreting pituitary adenoma (a.k.a. pituitary gigantism), which is the focus of the remainder of this article."
"The vast majority of cases of pituitary gigantism are sporadic, and diagnosed in mid to late childhood (e.g. 13 years of age 1)."