I'd personally advise against microdermabrasion treatments or a chemical peel - personal, awful experiences (I had terrible acne as a pre-teen and teenager). Expensive and painful.
I'm only 27 but I've recently noticed facial wrinkles, maybe it's from the weight loss, or maybe I just smile too much
Personally, I'm just saying, "Oh well!" as I don't mind them.
However, for you, I would second the facial exercises. I was once obsessed with preventing a double chin and was surprised to find that facial exercises actually made a (small) difference if I did them consistently. The rest of it may depend on your age, but hopefully your skin will bring back some once you're maintaining your weight.