PSA levels are usually considered to be normal at around the 4 mark, but they do tend to be higher than that in older men. That's why the level is only seen as an indication that something is wrong.
I don't know what the PSA levels are likely to be for this, but there is a condition called benign prostatic hyperplasia which is where the prostate grows and constricts the ureter. Treatment could be by drugs or minimally invasive surgery. Another possible condition, and again I have no idea what the PSA levels are likely to be for it, is prostatitis (hope I've spelt that correctly), again not a serious condition.
The scan will probably also include a biopsy which will be used to confirm whether or not he has cancer. If your Dad does have prostate he will also have to have a bone scan to check if any of the cancer cells have got out and migrated (when they do they usually settle on bone and keep growing). Treatment for prostate cancer is very successful if it's caught early, so keep your worry levels down until you know the results of the biopsy.