Here are some random thoughts for you to consider. From a sub male who loves to be denied. And someone who has found and experienced foreskin restoration. Just to give you some of my background.

I would love to be in your situation, where I was not able to climax inside my Domme. Of course I also want to cum when she gives me permission, but maybe your problem is close to another person's wish?

You say you are in your 40s. You didn't mention whether you are normal or circumcised, fit or out of shape. And you don't say whether masturbation is taking longer or more effort. So take what I am about to say as food for though, no more. I am not trying to start a debate about circumcision, just give you my experience and understanding in case it may help. I hope it will be useful as an alternative to your hypothesis that years of masturbation have resulted in this condition.

In my 40s, I vagually sensed a gradual decline in how easy it was for me to climax either by masturbation or intercourse. But since it was gradual, and since I am so good at masturbating, it was less evident with masturbation. And it was subtle, slow and I didn't really notice it much. Like when you have a puppy or child and someone comes to visit who hasn't seen you all for a while and remarks how big they have gotten.

In my late 40s I found out that it was possible to restore your foreskin by the same technique used by body modifiers and surgeons. Skin put under tension for long enough grows additional skin. I still don't know why I was so captivated by it back then, but I embarked on it. It has been successful, though I am not finished.

More importantly, I have experienced a huge increase in how easy it is to climax. In the past I would have to expend a great deal of energy and fantasizing to reach climax by my hand. Intercourse left me panting and wiped out. I even had to stop for rests at times for both intercourse and masturbation. Now I cum with ease and it is sensually relaxing. So it is clear to me that a normal penis with a foreskin works much easier and takes much less effort than a circumcised one. So it may simply be that (assuming you are circumcised) that you are at the point where things are getting more difficult for you in terms of reaching climax.

By the way, I have until 5 years ago, masturbated to climax frequently, my estimate would be more than once a day, sometimes 3 or 4 times a day, and I remember once climaxing 8 times in one day. I had sex relatively late in life (mid 30s) and had similar worries about masturbation causing problems when I got to have intercourse. I couldn't detect any problems.

Regards,