What can I do to tighten the lower half of my face in my early 40s? (Photo)

A short scar facelift is a great option for many people. The recovery & downtime is very minimal. There are usually no drains, most people can go out the same day, you can shower the next day, there are no scars behind the ears and you can wear your hair up anytime and most patients take no pain medicine. The result is usually the same in selected patients as a full scar facelift but it really depends on your exam.
Surgery is not for everyone. In today's day and age, there are many nonsurgical options to consider although surgery usually gets the most improvement specifically of the neck and jowls.
I would recommend that you see a board-certified plastic surgeon in your area that is a member of both ASPS & ASAPS and performs a lot of mini facelifts and neck lifts but also offers all the nonsurgical options such as injectables and laser treatments. Go over your concerns with them and make sure above all, you walk out of there with several options and an idea of the pros and cons to each of them as well as realistic expectations. 
I hope this helps and wish you all the best in your surgery and event. If it does, please take a moment to up vote this answer on the “respond” button on the top right. 

The contour of the jawline is relatively good, with no discernible marionette lines, but there seems to be some fullness under the chin.Because you are slim, it is less likely that the volume is under the skin and more likely that it is deeper to the platysma muscles.A neck lift procedure would be suitable to tighten somewhat the jawline and address the volume under the chin and together with the contouring under the chin can give you a balanced rejuvenation in the lower face and neck.

Thank you for your question.Based on the photo, you may be a good candidate for a Necklift. This procedure tightens the neck and jaw line areas. I would recommend having an in person consultation to be examined and determine what your best option would be. Good luck.

Unfortunately, the one photo, which does not even include the upper cheek region is not really sufficient for an adequate evaluation. However, from what I can see there is a suggestion of volume loss in the upper cheek region and likely volume depletion in the region in front of the ear--both of which are contributing to the loss of tightness and definition of the jawline and the formation of the jawline and angle of the mouth jowls. Happily, both these issues can be corrected in a matter of about fifteen minutes total (in experienced hands, of course) by the use of a volumizing filler to lift and reshape the upper cheeks coupled with another volumizing filler for the preauricular region and the jawline directly. Treatment typically engenders and immediate "Wow!" reaction. My choice in my NY office  would be Voluma XC for the cheeks and Restylane Lyft  for the jawline. In my Israel satellite facility where a far greater number of regulatory agency approved injectable volumizers are available, I would opt for Stylage XXL and Restylane Volyme, respectively. Be very cautious when evaluating the claims for this or that bells and whistles fraxel laser, radiofrequency device or ultrasound machine, as these heavily marketed devices are far more supported by device manufacturer marketing hype than hard science. Buyer beware. Make sure that you consult with a board certified aesthetic physician and insist upon seeing his/her personal before and after photos before agreeing to proceed. Best of luck.

FaceTite can internally tighten the skin in the lower face and neck. After all the skin has been heated and contracted, we shape the neck with liposuction to give definition and remove stubborn pockets of fat. In one quick treatment, we can tighten skin, remove fat, and contour the lower face, jawline, and jowls with only a weekend of downtime. Keep in mind that combination approaches will give you a more significant improvement as opposed to a single procedure. I recommend getting a consultation with a board-certified cosmetic dermatologist and facial sculpting expert. Best, Dr. Emer