As they get older, especially if you keep them with other SDs, which, obviously, you should, they start looking a little beat up. Not bad, but just obviously an older fish. There might be a place where a fin nip went a little too far, a scale or two missing on the head where they've run into things in their frenzy to swim away, etc. I would provide a photo just to be sure if you think it could be ich (any new additions? Any flashing or heavy breathing?) but otherwise, what you're seeing is pretty normal, IMO.