I'm 21 years old. What I should do about my chin and underfat? (Photo)

Young patients with double chin are usually excellent candidates for chin liposuction. The procedure permanently removes the fullness under the chin, thus correcting the double chin.
In my practice I routinely perform the procedure under local anesthesia. Downtime is about one week due to the swelling and the chin wrap that must be used for at least 5 days

For a double chin, InMode FaceTite with VASERlipo would give you the best result.
With significant neck sagging you would need a facelift / neck lift with muscle tightening (platysmaplasty). At the same time, I would recommend lasers (Fraxel, CO2, or Erbium) and microneedling RF (Fractora, Morpheus8, Intensif) to improve the crepey skin and wrinkles. Overall, the neck can be treated with a combination approach:
1. Microneedling and laser treatments for texture
2. Botox, Dysport, Xeomin or Jeuveau to help platysmal bands
3. Intensif, Fractora, or Morpheus8 microneedling RF for crepey skin and lifting
4. Injectable fillers like Belotero, Restylane Silk, and Juvederm Volbella to improve lines and folds
5. Face/neck lifting if sagging is prominent or premature, with or without platysmaplasty (muscle tightening)
6. Renuvion (J-Plasma), ThermiRF, and InMode FaceTite/AccuTite for internal tightening
7. Ultherapy and Thermage for external tightening
8. Regular Venus Legacy, Exilis Ultra, or InMode Forma treatments with facials to maintain tightness
9. PDO NovaThreads or Silhouette InstaLift cone threads for lifting and long-term collagen production
See an expert for a formal evaluation and to develop a personalized treatment plan based on your individual situation and goals.
Best, Dr. Emer