I know a guy in his middle 60s who still pushes some heavy iron. OK his Skin is a bit saggy but still has an impressive build. 
Many things can cause sagging skin; age, of course, weigh gain coupled with weight loss, smoking,genetics and too much ultra violet exposure, etc. As much time as I spent laying out in the sun when I was younger, my skin should be very wrinkled. For some reason, probably genetics, it is not that bad for someone my age. One possibility is that I have very oily skin.