From your photo, the fullness appears to be mostly in the lower cheeks and soft jawline area rather than a large, obvious fat deposit under the chin. Liposuction can be helpful for submental fat under the chin and sometimes along the jawline, but it is not usually the best tool for slimming the central cheeks. Overdoing fat removal in a young face can also create hollowing or premature aging later. The best option depends on what is creating the roundness. If you have excess fat under the chin, submental liposuction can sharpen the neck-jaw transition. If the fullness is mainly buccal fat, buccal fat removal may slim the lower cheeks, but it should be conservative and is not right for everyone. If the issue is a small or set-back chin, chin filler or a chin implant can make the jawline look sharper without removing fat. If the jaw muscle is wide, Botox to the masseter muscles may help. Sometimes a combination of small changes gives a better result than one aggressive procedure. I would recommend an in-person consultation with a facial plastic surgeon or plastic surgeon who can examine your skin thickness, fat distribution, bite/chin projection, and masseter muscle size. Ask specifically whether your goal would be better served by submental liposuction, conservative buccal fat removal, chin augmentation, jawline filler, or no surgery at this stage.