The amount of oil an individual produces is determined genetically, with a hormonal influence. During adolescence an increase in the level of sex hormones, known as androgens, awakens the oil glands, which in turn produces sebum (oil). For women, hormone changes occur not only during puberty, but at the start of each menstrual cycle.
Although oily skin will remain oily throughout your life, as you age, oil gland activity will decrease. In most patients, this decrease in activity starts in the 4th decade of life.