by the spotting on face and body plus the purple tint to the body, females tend to lack the face spotting and have a yellowish base color. also males have higher head profile and body is more elongated than females, the females body is more round.
when caught from the wild or natural setting size doesnt really tell age. usually 4-5 inches tank raised is anywhere from 6 mo to a year. in the wild they can be 1-2 years old. that guy looks over a year. usually in the wild they grow slower due to having to find their own food, the domesticated fish are fed on reg basis.