Jawline improvement wanted for young, thin, average male—what are my options? (Photos)

Your jaw line seems to have a little less prominent angle.  Although it looks not too bad, if you would like to make it a little more defined, you can also consider having an acculift  on those area.  This is using a liposuction together with laser.  You can reduce the volume of the fat in those are to make them look more defined.

Your problem is that you do not have a well defined posterior jaw angle.  Males ideally have a square jaw, with a prominent angle.  This can be recreated quite easily with fillers, but would require annual treatment.  Fat transfer can also be considered for this area, which will last longer.

You could improve jawline definition using hyaluronic fillers like Restylane Lyft. This will sharpen the jawline and improve the chin width as well should you also choose to have the chin treated.

From your photos it would appear to be a fairly simple and low cost injection of Radiesse in such a way as to slightly square off the chin and sharpen the sweep of the jaw in a masculine pattern.  This usually will last 9 month to one year and can be easily repeated.  Doing permanent procedures such a chin implant before you know if you are happy with the change is appearance is best put off until after you have seen the affect of the filler.

I think you would benefit from reJAWvenation(TM), my trademarked procedure to enhance the jawline. I would use either Lyft or Radiesse along the jawline with cannulas to minimize risk and bruising. It take less than 10 minutes and gives a more defined and wider jawline. I lecture across the world on this procedure. I would also make your chin a bit more prominent. If tightening is needed, Infini or Genius can be used, which is RF microneedling. 

jawline augmentation is a long term solution and can be designed for proper facial balance. Defining the jawline is common for some of us and extremely esthetic. Fillers are a short term solution and expensive over the long term. Consult a cosmetic facial surgeon who can show you many examples.