I believe it's the sun and good genetics. I've got decent genetics (I think?) but I worked outside all of my 20s and 30s. I used sunscreen religiously but squinting (due to sun) and the like also plays a role. It's hard to remember to reapply in the middle of a 12 hr day, when there's work that needs to be done.

I'm exaggerating how wrinkled I am, but I definitely got crows feet and forehead wrinkles.