Skin-Care help!!!! early 20's?

First of all, don't gain and lose a lot of weight. Unfortunately, it's hereditary, so you are going to have to really work at it to keep yourself from getting a double chin and then ultimately loose flabby skin underneath the chin. Moisturize and exercise and drink lots and lots of water. Don't stress out too much about it, after all you are only 20...just take care of yourself now.