They start at around 40. They plummet off a cliff after your late 40s.
Or maybe that's just me. 
I scrutinise the faces of all my friends who are of similar ages give or take a couple of years and I am increasingly of the opinion that while smoking and too much sun is absolutely the worst thing for your face, the rest is largely down to genetics and you can't change it.
I have friends who drink like fish (alcohol, not water) and their skin is lovely. I have friends who exercise really hard and try to watch what they eat and remain fat. I have friends who don't do any actual exercise at all and look fabulous. I have friends who exercise like demons and are very thin but they will pile the weight on the second they stop.
I have friends who look remarkably unlined and un-jowly for no reason I can discern and others me who drink only moderately, have never smoked, spend a fortune on good quality skincare, take supplements, never leave the house without slapping on the SPF 30, always wear a hat in the sun, eat a diet rich in omega fats, lots of nuts and seeds etc., yet I still look like an ancient bloodhound who has had a particularly hard life.
But then I look at my mother and I see why.
I am going to have a facelift.