Your immune system changes as you age. In some ways not always for the worst.
I suffered allergy induced asthma for over 20 years (into my 40's). In my 30s a doctor told me it would improve when I got into middle age. I can do things now, without meds, that I couldn't do when I was 25 and heavily medicated. Being able to breath is a wonderful thing.
I am doing the opposite. I just developed an allergic bronchitis this summer, to bleach of all things.