If it's not older than 2 years, it probably isn't old age. It doesn't look like finrot. Finrot would have a black edge along the fins, or even red from bleeding. It looks more like stress. What is the water temperature? It could be from poor water conditions, or even parasites from frozen or freeze dried foods. Bloodworms is a carrier of parasites, as well as other freeze-dried foods. A good salt bath could help if there are external parasites, but you will need a med to treat for internal ones. I'd try to do 100% water changes every day to see if he perks up. If that doesn't help, then treat for parasites.