I would agree with that. But what a time to realise it if you didnt before. Its like trying to play catch up.
Sadly it will take a while to have an affect.
There is a study out of Kings College, London from 2-3 years back that looked at immune function of aging athletes (cyclists) vs. Sedentary vs. Healthy young adults.
The basic summary was that the older cyclists who had remained active throughout their lives still had the immune function of the young adults. Where as in the sedentary older adults their immune function had significantly declined. The sedentary folk had a much shrunken Thamus, and their T cells weren’t as numerous or effective as in the other groups.
Thus the decline in immune function isn’t just due to aging, it is due to a sedentary life style and time.
Keep active throughout life, retain the immune system of your youth.