Centropyge angels are protogynous hermaphrodites. They are female first then the dominant one turn male. Centropyge will also revert sex change back to female if there is a more dominate fish in his territory. These are well documented, but may not be well known.
IME, and observation, single Centropyge tend to stay, or revert back to female and only turn male when there is a smaller angel in the tank. I am keeping a single Flame angel in my tank for 2 years by herself. She is still a female, and is a mature fish. I put three young and small Flameback angels together and within 2 weeks I already have a male, the largest of the three.