Think about it. I don't get the flu either and don't get the shot. I believe that the older generation are more disease resistant because we had to survive everything as children and young adults. Our immune systems are much stronger than the youngsters who have been trotted to the doctor for antibiotics every time they sneeze, and get shots to prevent the childhood diseases. They have no natural resistance. Hot house plants.
A lot of us also had to survive "recruit crud" in boot camp, where you got exposed to every strain of cold known to man.
You have a very valid point.