Lack of disease and disease treatment. Mostly Vaccines. I got sick like 2-3 times grand total growing up, and only once any more than mildly. My parents and their parents all got badly sick more than that growing up, and both have stories about being on deaths door, e.g. my dad got german measels at 17 and was bed ridden for a month; I didn’t get my last growrh spurt until I was 19.