Could a narrow bite cause sagging cheeks and jowls? I had braces age 12-15 but never wore my retainer. Now I'm 26.

There is not enough information in your photos but you do have a long narrow face.  I am curious about where the teeth are.
I suspect that you have dark buccal corridors and a narrow v-shaped maxilla.  This will not offer eithe bony or tooth support for the soft tissues of your face.   I would expect you woul be an exellent candidate for a DNA Appliance and Epigenetic orthopedics/ orthodontics.

Moving teeth, especially extracting bicuspids before moving the teeth, will cause significant facial changes. This is why no one should allow teeth to be extracted or moved before the doctor proposing to do so can answer three extremely important questions with a great deal of confidence: 1. How will your proposed treatment affect my facial aesthetics? 2. How will your proposed treatment affect my TMJ? and 3. How will your proposed treatment affect my airway? If you are not completely satisfied with the answers, find a doctor who can give you the answers that make sense and fit within your treatment objectives.The answer to your specific question is yes, moving teeth can definitely affect facial aesthetics. Can you simply move teeth to fix the problem? Probably not. You will need to develop your dental arches. Find a dentist who understands epigenetic orthodontics and make sure you address the three questions above before accepting any treatment recommendations.Good luck!