Disclaimer - Not a Dr.
Background - I have broken my L4 & L5 vertebrae twice each, both times stress fractures as part of college athletics. As a result of these injuries I was forced to take 10 years off golf as swinging was excruciatingly painful, this is also when my kids were slammed with activities, so golf would have been limited anyway. I finally started playing regularly again last year, pain free.
I currently carry 3 different Strength & Conditioning certifications, and regularly work with people who have tight backs as well as other aches and pains.
In my time I have found that back issues tend to fall into 3 categories. I will explain what those look like to me, and my general training model for each of these. I won't be providing any specifics as I shouldn't since I don't know the fine details of your, or anyone else's, pain and limitations.
Category 1 - Caused by tightness in the connective area that manifest itself as back pain and tightness.
Category 2 - Caused by a lack of centerline(core) strength, that forces the lumbar erectors to carry most of the load.
Category 3 - Caused by postural limitations that keep the lower back in a state of flexion at all times.
Category 1 - This usually looks like someone with tight hips, tight ankles, hamstrings that are constantly tight. In all fairness this is 90% of the adult population and something that most people just ignore outside of a PT session. A little bit of stretching and mobility work can go a long way.
Category 2 - Every single muscle that keeps you upright works together. If you have a weakness in one, then the others are forced to do more work. It is especially common as we age for issues to arise as cumulative wear and tear start to compound as our chemical make-up changes. Some light strength work under a professional eye would be recommended, not only for golf, but for life.
Category 3 - Ever see an elderly person using a walker who's eyes are always looking down? Most of us have the same issue, just not to that extreme. Stand up straight, shoulders back and under the ears. There are obviously stretches and exercises to go with this, but just being conscious of posture will go a long way.
Finally, the discussion of Cortisone shots. I have no personal experience with them ever and as such can not make any commentary.
Best of luck, I hope you were able to take something however small from this.