I believe the hypothesis is that age may very well play an important factor in the development of the immune system. What your body learns in the first 3-4 mont

I believe the hypothesis is that age may very well play an important factor in the development of the immune system. What your body learns in the first 3-4 months of your life is not equal to what it learns during the next 6... It's moved on to other things. That's actually how the brain works. Once you form a habit, for example, you follow the developed pattern (now moved outside of the conscious level) without thinking about it much anymore. It's how people learn how to walk, talk, and basically do everything else they once learned in life with relative ease... It's the brain's method of freeing up resources for other, new things. It doesn't sound all that implausible to me that certain other mechanisms of the body might perform in a very similar way.