It depends on the individuals. You'd need to start off with seperate cages and supervised time together and. There's no guarantee they'll even get on let alone be safe left alone together.
Conventional wisdom is that once fully mature (around two years old) the female's iris will be red and the male's dark brown or black. Unfortunately it's not a surefire way of sexing as there are plenty of females out there with dark looking eyes. If you were planning on getting a second bird and you don't want to risk putting a male and female together a dna test would confirm the gender.