Dr. Greene's Answer
As with underarm odor and hair, oily skin and hair typically begins anytime after the 8th birthday in girls and the 9th in boys, though it is often not seen until much later. The age for this varies even more than other parts of growing up. Even though almost all teens will eventually develop at least a pimple or two, as many as 20% of kids will have dry skin and hair throughout puberty. The average age to develop acne is about 12 ½ in girls and almost 14 in boys – but this commonly varies by years in either direction.