Angels are tough to sex - many times the males will get a "bump" on their forehead, the females usually do not (I would say that about 80% of my males have this bump). It is more prominent as they mature. Also the shape of the bottom fins attachment to the body can help identify them. The females tend to be a more straight attachment, the males are a little more curved. All that being said, I have some that are just the opposite. I am right maybe 75% of the time. When they are younger, the largest, fastest growth seems to be more of the males than the females. When I pull some from a batch to grow as potential breeders I used to pull the largest, fastest growing ones - I had a growout tank of almost all males. Now I just look for fin shape, color, body shape and I am getting some females w/the males.
HTH,
HTH,