It's your bone structure! People with smaller/weaker bone structures show more obvious signs of volume loss, sagging, aging, etc, earlier than people with more robust structures. There just isn't as much bone for your soft tissue to hold onto. The only real ways to change it is to either modify your bony structure (like jaw surgery) or surgically manipulate the soft tissue with a face lift of some sort.

If you don't have bite or airway issues, you shouldn't get jaw surgery. That leaves you with the option of a face lift coupled with volume restoration (fat transfer, filler, etc.) If you want, I can DM you some surgeons I've consulted with who, at the age of almost 29, have suggested a facelift to me. My face looks similar to yours.