What to do if i have never broken a bone or been ill, never had a cold, am i invincible?

Healthy: You are young and healthy and very fortunate. Keeping up a healthy immune system includes eating well, sleeping, exercising, avoiding excess alcohol, stress, smoking, illicit drugs and keeping good hygiene and hand washing. A healthy immune system will keep you from getting sick. However you are not invincible. See your doctor for a yearly check to be sure you stay healthy. Best wishes.