Hi, I will move this thread to the Nonsurgical room for you
Some types of spinal deformities sometimes do run in families (Adolescent Idiopathic Scoliosis does so more often than other types) but not every case does. Scheuermann's Kyphosis can be diagnosed from an x-ray, yes - the wedge-shaped vertebrae causing the spine to arch can be seen on a lateral film. Otherwise you can tell whether a curve is purely postural or not by seeing if you can completely remove the kyphosis by forcing yourself to stand up as straight as you can. For those of us with structural curves, it isn't possible to completely straighten our spines.
I think it is very unlikely that you still have spinal growth remaining at 20, although some males may still have a little growth remaining at this age. In your position I would try exercises rather than a brace. Even structural curves have a small postural element to them so it's often possible to get a bit of correction with targetted exercises.
In order to get a good brace you would need to get one prescribed for you by a doctor and have it fitted by an orthotist, and this can be very expensive. Be wary if you do get a brace as there are a lot of untested designs around. Some braces will give an encouraging in-brace correction but there is no guarantee that the spine will remain corrected once you stop wearing it.