Marilyn Diamond is living proof that you can be 68 years old and look decades younger. A healthy living expert, she is coauthor of Fit for Life, which has sold millions of copies. She collaborates with her husband Dr. Donald Schnell. Dr. Donald Rock Schnell suffered a diabetes-induced heart attack at 55. Doctors gave him up to 5 years to live. The Young for Life program is an adaptation of the plan that saved his heart and created his rock-hard body.