What should I do about my festoons/malar mounds? (Photo)

You don't appear to have festoons but you do have malar mounds and nasojugal grooves (tear troughs). The best thing to treat this in your age group is a filler in the nasojugal groove. This could be an HA filler like Restylane or Juvederm or your own fat. Book a consultation with a board-certified plastic surgeon near you to see what your best option will be. Hope that helps! 

You do not have festoons but a combination of malar mounds with tear trough formation (naso jugal groove). Subtle fat injections or filler can be used but you need to be careful in this region and you need to consult with a PS with experience in treating this. 

Thank you for posting your pictures. The line you are seeing dividing your lower lid from your cheek is known as the naso-jugal groove. This line gets accentuated when the malar fat pad descends secondary to gravity pulling forces and lack of structural support. The fact that your canthal tilt is neutral or slightly negative (lateral corner of your eye is slightly lower), tells me that your cheek structure has less support and you are prone to see early changes in this area due to pulling gravitational forces. Fillers are a great way to create a lift and restructure the cheeks and will help eliminating the naso-jugal groove. Radiesses and  Voluma XC are temporary options (no surgery required), but if you like the results and would like more permanent results, then you can consider fat grafting. Hope this was of some help. Good Luck!