Developing healthy habits when you're young can help you live a longer life and reduce your risk for many illnesses like heart disease and some cancers. The choices you make during your teens, such as choosing to spend time in a tanning bed or taking an interest in long-distance running, can establish patterns and begin habits -- both good and bad -- that will impact your body through adulthood. Youth is a preparation for old age in more than education and learning life lessons. The human body, through use or neglect, learns lessons, too. Adopting positive habits and avoiding destructive ones is a way to start on the path to a more active and happier life.