I'm in my late 50s.  When I first started playing as a kid, I adopted a strongly-backhand grip, and almost couldn't hit a forehand if I tried.  

Years later I sustained a very serious injury to my playing hand.  The operation involved a tendon transplant from my wrist as I recall. At some point I picked up a paddle again, at least now my grip was not so BH-dominant. So I played for years off and on.  I moved to a different state. Eventually I got in touch with the local coach in this metro area, and got involved with leagues which I still am, though not that diligently.

The previous winter I actually gave up playing right hand because I was so frustrated with this same backhand issue.  I applied myself to learning left hand, and I did enjoy it partly because it was fun and motivating to actually start just about from scratch.  I no longer had ingrained bad habits.  So I got a better practical understanding of technique.  There were a couple moments of "aha! That's why coaches say to do that."

 I took personal lefty lessons from a top coach.  After months I had to quit.  That was, believe it or not, because my (aged) left pinky it appeared could not stand up to being wrapped around a paddle that often.  I now haven't played lefty for around 8 months, and that pinky still does not feel quite normal (it is stiff in the mornings).

So it was back to RH.  Now I found I could apply some of the "first-hand" LH stroke knowledge to my RH.  A couple times in the process I grabbed the paddle LH (pinky extended!) and basically "watched myself" hit a few shots.  But I also decided I had to fix my very long-term issues with my RH grip.  I decided it was too loose, and it was out of position. That took a long time with grip-experimentation on my robot.  After awhile I realized it was somewhat trying to deal with two conflicting issues:  I needed to habitually grip the paddle more firmly, but I needed to be quite relaxed to  be able to execute a BH.  What I ended up doing, was in between each shot, I would momentarily tense muscles, then relax for the shot which really helped.

A few weeks ago I did go to a clinic with the top coach in my state and asked him to look at my basic strokes, he had no changes to suggest.  Thanks so much for all of your replies and suggestions.  What Kreanga was doing around 2:58 is almost exactly what I tried recently.

I'm sorry I didn't give details such as my ancient operation (around 30 years ago), but I've thought about making this posting for months, and including that stuff made it such a long post, plus I suppose I am a bit reticent.

I do take care of myself pretty well.  I'm an obsessively healthy eater.  (I actually keep vitamin C powder at my desk at work, and have a tiny bit maybe every hour or two.  I make what's called chicken bone broth and have some daily.)  My ankle is a little tender at the moment, but normally I walk most days of the week.  And work in short sprints during the walks (one of the things I'm not doing right now).  Sometimes I get lazy, but try to do things like pushups, pullups, air squats, planks.  I've lost about 35 pounds in the last 8 years.

It is true that normally I do virtually no stretching before play or practice, but of course this BH issue has all my attention and if stretching does the trick I'm all for it.  I think conventional stretching is a little over-rated from what I've read. Maybe it's diet that allows me some relative freedom from injury in recent years.  I'm sure that sounds strange to some.  My rating I suppose would be around 1200. That same local coach recently told me he knows of players much better than I, where he saw the player not be able to do a stroke properly until about 30 minutes of steadily trying the same shot.