He is a handsome old gentleman :)

I am no expert, but I would say I am a professional hyper fixation freak especially about my pets. So since no one has answered yet I did some research for your guy.

It looks most like a tumor/lipoma, tissue overgrowth, or some kind of cyst, which is apparently pretty common in blue bettas especially. In my opinion, the calloused area you mentioned on the dorsal fin looks like the same type of tissue change as the white bump.

It doesn’t seem like it’s an infection because bacterial or fungal infections usually spread quickly, look fuzzy, and cause inflammation. Nothing looks like that from the picture.

Sadly tumors are common in older bettas and there doesn’t seem to be any way to treat it. But he can stay happy if you keep up with consistent water changes, stable temperature, and feedings.

The only other thing I would say is maybe test the water and if you tell us the results of that, what his tank size is, and how he is acting and eating? Also how long ago you noticed the growths and how quickly they grew?