What procedure would you recommend for light sagging in the lower face for someone in their early 30s? (Photos)

You appear to have a quite youthful-looking face, although it's not possible to gauge the tone and quality of your skin from the photos alone. I would first suggest following a daily skin care regimen, if you're not already doing this, following the recommendations of a dermatologist. As for the slight signs of aging you've mentioned, you could consider getting injectable fillers for the minor lines around the mouth. Good luck to you. 

Your skin looks fine although you may have more cheek fullness than you desire.  One option is a buccal fat pad excision.  It can be done as an office procedure. 

Thank you for the photos and your questions. Generally, at your age, skin care is the best place to start. This would include a complete program of tretinoin, sunscreen, moisturizer, etc. Beyond this, gentle treatment with fillers for early marionette folds could be considered. Botox can be used in the masseter muscle to make the jaw look a little slimmer -- though this is not specifically related to aging. As a final step, for patients who develop early jowls or laxity along the jawline, ThermiTight can be a fantastic solution. This is a minimally-invasive radiofrequency treatment that tightens the skin and reduces some fat volume. Take care!

It appears from your photos that fillers would be all you need at this time.  You have a pretty face and if you do too much you run the risk of looking over done or fake. Be sure to consult with a board certified plastic surgeon. Good luck!

Based on these photos you may consider conservative  correction of corners of the mouth (Marionette lines) and nasolabial folds with fillers. Full face photo or clinical exam would reveal whether additional volumization of cheeks or chin would benefit re-creating round, youthful face.You should consult an experienced board certified plastic surgeon with good reputation in facial rejuvenation to discuss your options. Try to avoid "certified injectors" of any kind. Good luck.