I think smoking, sun and stress are probably the key factors - not alcohol so much unless it's really excessive.
Comparing dh's 2 nans is amazing - one who has smoked all her life and the other who hasn't. The one who has smoked has a face like an ordnance survey map () and the other has a face that is so unwrinkled you wouldn't believe it if you saw it. She swears by Oil of Ulay.
Even at age 32, myself and my SIL I would say have got quite different skin - she's a smoker and I'm not and I think mine looks significantly healthier. And dh's Mum looks quite a bit older than my mum - again, MIL smokes, my Mum doesn't.