While things like nutrition and exercise influence whether people age prematurely or late, genetics also play a significant role. I have a good genetic heritage. There's almost a generation gap between me and some of my peers. I've been exercising regularly since childhood. I've been particularly mindful of what I eat for the last 10-15 years. I don't drink alcohol or smoke. When we look at people who age quickly, we see a higher prevalence of alcohol and cigarette use.
And too much sun, at least for the look of skin.
Genetics is an important part, but on average, it is pretty basic to do what is right most of the time, for most people.