M.K.
My son was 5 when he had his surgery, did you ever noticed that your son only had one?, sometimes they can have them then they can retract up inside the body and get stuck.
the case with my son was that the tube turned on itself and cut off the blood supply and the testicle died, they removed that then tacked the other in place so that the same thing could not happen, his testicle is normal and healthy, and a little larger, apparently when you remove one, the other will compensate,
it is really unusual to have it diagnosed so late - usually you will notice during diapering that there is only one, which is why I was asking if you noticed or not.