I'd agree that it could be either fin rot or tailbiting. With fin rot, the edges of the fins can be discoloured (darker or lighter from what I've read). With tailbiting, in my experience, the fins are just ripped up and ragged. It's hard to tell which it is since the pictures are small.
I will however disagree with bettafix. I've heard more negative about it than good. Treating with medications for fin rot should be avoided unless it is extremely persistent/advanced in my opinion. For now, I'd say just keep the water super clean - his fins will heal themselves with time and clean water! Either way, whether it is fin rot or tailbiting, you want to keep the water super clean since the injured fins from tailbiting can turn into fin rot.
If you want to treat with something for possible fin rot, aquarium salt is a good start I've heard. I don't want to recommend on dosing as I've never used it, perhaps someone else can advise on that.