Although kicking the butt has major and immediate health benefits for women of all ages, the benefit is greater the earlier in life a person quits. People who stop smoking before the age of 35 years have a life expectancy that is similar to nonsmokers.
The health dangers of smoking are reversible, but for some causes of death, the reduction in risk occurs over many years. For example, it takes much longer for the excess risk of death associated with respiratory disease and respiratory cancers to approach that of a "never smoker:" 20 years for chronic obstructive pulmonary disease (COPD) and 30 years for lung cancer.
However, for some diseases like coronary heart disease (CHD), the major precursor to heart attack, there is a rapid decline in risk. The excess risk of CHD caused by smoking is reduced by about half after 1 year of smoking abstinence and then declines gradually from that point. From 5 to 15 years after smoking cessation, stroke risk is reduced to that of people who have never smoked. At 15 years, the risk of coronary heart disease is similar to that of people who have never smoked. Another smoking-related disease that has a rapid decline in risk after quitting is cervical cancer; the chance of developing cervical cancer is substantially lower among former smokers in comparison with continuing smokers, even in the first few years after cessation.
All that said, it's best to never to start smoking in the first place. Lung cancer has surpassed breast cancer as the leading cause of cancer deaths among women in the United States, with smoking directly responsible for 87% of all lung cancer cases in U.S. each year. Smoking also causes heart disease, the #1 killer of women in the U.S. Smoking causes or contributes to chronic respiratory diseases such as emphysema and chronic bronchitis, and many other kinds of cancer, including cervical cancer. It also increases the chances of stroke, blindness, early menopause, osteoporosis and infertility.
The bottom line: Don't start smoking. But if you do, some of the damage is reversible, and it's never too late to stop.