Hey there,
Yes his tail has been pretty damaged in the past but by giving him plenty of regular water changes to maintain good water quality and providing him with a good diet he has every chance of full fin regrowth. I have had bettas in the past where their fins did not recover but they were rescues and half dead when I got them, their fins were damaged beyond repair (way way worse than your boy, their fins had gone all stiff and dead looking and there was no new fin regrowth) however they did survive and live a reasonably happy long life. Your boys fins don't look too bad, they appear to be healthy so keep his water clean and give him a lot of time and you may be surprised at his progress