What ages healthy people the most? Wrong food or exercise? Genes?

Difficult call. Exposure to uv radiation (sun), tobacco use, and excess alcohol or drug use are the things doctors see that make people appear "older than stated age". After avoiding those insults, to me, the *right* food does most to reverse aging. Eating right can even turn on the right genes to promote a healthier you. See books by drs fuhrman, mcdougall, and barnard or go to forksoverknives.Com.
All the factors you . Mentioned. So wrong foods, or eating too much of it; lack of exercises; genetically you could be predisposed to ageing early.