Correction of early jawline sagging
Surgically, the jawline is corrected by facelift procedures. Since your young age however, you might want to try miniminzing the appearance of the jowls with an injectible filler or trying laser. Any number of fillers can be used to hide the early sag by either being injected in front or behind the sag. Sometimes, a little volume in the cheek can help alleviate the early appearance of droop.
Additionally, lasers can provide a degree of skin tightening. Again...