Acromegaly and gigantism aren't the same thing. Acromegaly is excessive growth of the extremities--fingers, toes, jaw, and nose--caused by an overactive pituitary gland. Acromegaly shows up in adult patients whose growth plates in the long bones (ie: arms and legs) have fused. Acromegalics are not classic "giants" for this reason: fusion of long bone growth plates prohibits the growth hormone GH from entering the long bones, which is why there is no increase in height; thus, the extremities become larger. Therefore, patients who are diagnosed with acromegaly are usually in their thirties. Also, the etiology of the disease progresses very slowly, so its effects on men and women who have it come about very gradually. (For this reason, acromegaly is usually undiagnosed for many years.)
Gigantism is abnormal growth or development of the body or its parts. The difference between acromegaly and gigantism is the timing of the disease. When the pituitary gland has tumors before the growth plates have fused, as in the cases of adolescents, this is gigantism. Because the growth plates are still open, especially in the long bones, 'giants' have increased stature as well as enlarged extremities. They are slightly better proportioned than acromegalics, having not only large hands, feet, jaws, brows, etc., but the height so characteristic of mythological, or Biblical, "giants."