I agree 40 and 60 can look similar but from what I've seen, being young at 60 is due more to taking care of yourself than genetics.
At least hair loss and going grey is genetic. I am sure being overweight etc plays a major role, but I wouldn’t rule out a genetic component to most signs of aging.
Balding isn’t universal, a friend of mine is 70 and looks 50 with a full head of hair that not full grey, it’s kind of freaky. He’s still working construction and carrying heavy loads etc. Meanwhile I started going grey at 20.