I could see that interpretation.
For me though, I rarely ever get sick. I've never had the flu, that I'm aware of. If I catch a cold it's just congestion for a day or two. I've never experienced the body aches that people talk about. Never had strep throat or many of the things that many contract. Hell, I've never even had a headache, not that that has anything to do with immunity. I have a hard time equating that to anything other than being hit in the head. I did have measels and chicken pox as a youngster, but don't remember them being too bad. I've only had any kind of food sickness maybe twice. The same goes for my Mother and my Brother and Maternal Grandfather. Not the same for my Father or my two siblings that have passed. They would be bedridden with the flu and other issues, and it was obvious they were really sick. Their symptoms were always bad.
Luck of the draw I guess. As an example I'm feeling pretty good today. Congestion is much less and scratchy throat is almost completely gone.
My Mother is experiencing poor health these days, but that has much more to do with smoking for decades, heart issues and macular degeneration.
I'm not of the opinion that my immune system will be much help in the aging process though. Getting old can't be helped.