At least 6 years old, and he has to be in good breeding condition which means eating organic pelleted diet, no human food, and has had a recent Avian Vet check to make sure he is healthy.
Since diet is so very important, it will take up to a year to even begin to see the kind of improvement in your bird so he would be ready for breeding.
Here is a link about how to go about changing from all seed or junk pellet diet to the organic pellets found here: Switching Birds To Pellets article