Would I benefit from a facelift for the lax skin under my chin? (Photo)

Thank you for question and photos. It appears that you have submental laxity, and no evidence of jowling. Options include a platysmaplasty, which is a short scar under your chin, or posterior neck lift. Your lower face looks great, and I would avoid a facelift at this time. Consult with a board-certified plastic surgeon to get another opinion.

That is loose skin overlaying one of the platysmal muscle bands. I would recommend seeing a REAL plastic surgeon certified by the American Board of Plastic Surgery (ideally with 6 years of integrated plastic surgery residency training and ALSO a 1 year aesthetic fellowship accredited by the Aesthetic Society). I would recommend a necklift only in your particular case; you are one of the few individuals who would be able to have a submental incision only to address this issue.

Happy to provide a second opinion!
I often see patients with similar concerns–young, healthy and aging well with just a small amount of lax skin under the chin that bothers them. It is becoming more and more common for patients to seek surgery to correct those very first signs of skin laxity/sagging to maintain a youthful appearance throughout their younger years.
Your photos show that you could benefit from a neck lift or face lift. You are right about the skin laxity being the main issue rather than the platysma bands. However, the platysmaplasty is an important component of any neck or facelift to achieve a sharp jawline and maintain results by tightening the underlying tissues. It is difficult to tell without assessing in person whether or not a facelift is the best option as opposed to a neck lift but judging by your photos, you likely would do well with a neck lift alone.