I took a look at your photos and I honestly can't see anything wrong with your boy. The black colouring around the edge of your bettas scales are simply his colouring...... when a betta has black edges to their scales they are known as a pineapple betta.
His fins also look okay to me, he is a veiltail betta and as bettas age their fins sometimes change slightly in shape causing them to look a bit messy but he has no signs of fin rot that I can see. Most fin problems begin as a hole or split in the fins, they also sometimes get black edges to the fins and sometimes red streaks. Your boys fin do not seem to have any of these symptoms.
If you are still worried about him you could give his tank an extra clean and add some stress coat but from the looks of him he is just fine.