I'm 26 Years Old and the Skin on my Neck Has Started to Sag?

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

I recommend a combination
of Pelleve and Nectifirm cream to address skin laxity in the neck region.
You will need 4-6 Pelleve treatments and you will need to use Nectifirm
twice a day for at least 2 months.

You may be too young for a necklift. That being said, the Ultherapy neck lift with microfocused US is an excellent option if you feel that your neck is beginning to show signs of age. Best, Dr. Karamanoukian Los Angeles

     It would be hard to speculate without an exam.  Sometimes a neck lift is appropriate on younger patientsFind a plastic surgeon with ELITE credentials who performs hundreds of
facelifts, necklifts facelift revisions, and facial procedures each
year. Then look at the plastic surgeon's website before and after photo
galleries to get a sense of who can deliver the results. Kenneth
Hughes, MD Los Angeles, CA

Thank you for your question. See your Board Certified Plastic Surgeon and determine if your problem is muscle of skin related. Then you can determine a plan of therapy for your neck. I hope this helps.

The first step is to develop a great skincare routine using medical grade skin care products like Transform MD. An experienced aesthetician can customize the right product combinations for your skin. You can also consider treatments such as Moprheus8 to treat premature sagging. Morpheus8 combines RF technology with microneedling to improve overall skin tone and texture. I've included a video I hope you find helpful.

ThermiTight applies the "science of heat" with radio frequency using a pinpoint wand right under the skin to target areas that have lost elasticity. With ThermiTight you can expect increased collagen production as well as tightening of the overlying skin of the neck.

Please see a local plastic surgeon for an evaluation of your concerns and an exam so options can be provided to you on what would work best for your expectation.

It is rather unusual to have age related neck changes at 26.  Commonly, some neck or facial fullness is secondary to weight gain, genetics or structural craniofacial deficiencies such as weak chin.  You can save your money by avoiding most of the "non-surgical" neck lifts and topical treatments.  They are not effective, particular at your age.  Consult a reputable Plastic Surgeon in your area for a proper assessment and recommendations. 

Non-Surgical Neck LiftYour non-surgical options are dictated by your specific
needs which may include any of the below measures:1)improving banding: Botox2)improving under the chin fullness: Liposuction with oral
sedation3)improving skin looseness: VIORA REACTION radiofrequencyA consultation would allow a doctor to customize your treatment
plan.