I have heard anecdotally that men last longer as they age, but I always thought it was a gradual thing.
You said, though, that you have to jack off until you're sore to cum. Perhaps you're using too much grip? Not enough lube? There are a lot of men out there who use kung fu grip when they beat off, and I can see how that could be desensitizing your dick. If that is the case, perhaps try to loosen up and enjoy a lighter, longer touch?
I say that because I have an ex who used to practically strangle his johnson to get off. He said he'd had to do that more and more as time went on, just to get off. I figured maybe he'd started an arms race between his hand and his dick, and got him to ease down. After a few months his sensitivity started getting back to normal and I didn't feel sorry for his dick, any more.
Having said that, though, a little increase in stamina over time is totally natural. And isn't that a good thing?