You asked whether "degenerative disc disease at L5-S1" is normal. It is not normal, but it is not prostate cancer either. That finding is worth discussion with a doctor specializing in bones.
I'm not sure what "heterogeneous marrow signal intensity" means; it may be normal. Perhaps someone else knows. You could call the doctor and ask.
Regarding "extracapsular disease," I believe that refers just to the area just beyond the capsule of the prostate rather than the whole body beyond the prostate. Of course it's a good finding as it suggests the capsule has not been penetrated by the cancer. (Cancer can also hitchhike out of the prostate via the lymph and blood systems.)