At 42 and not overweight, this area can come from several different things: a small pocket of submental fat, skin laxity, platysma banding, chin projection, or deeper neck anatomy. In the photos, there appears to be fullness under the chin with some loose neck skin or banding, but an in-person exam is needed to tell how much is fat versus skin and muscle laxity. Kybella or small-volume liposuction can help when the main issue is fat and the skin still has good recoil. Filler or a chin implant can improve the profile if the chin is underprojected, but it will not tighten loose neck skin. If there is meaningful skin laxity or platysma banding, a neck lift, sometimes with lower facelift support, is usually more reliable than injections alone. A consultation with a board-certified plastic surgeon can sort out whether a nonsurgical option is realistic or whether a surgical neck/lower face approach would give the cleaner contour you want.