My guy bred with just about everything in sight at 6". If I remember correctly that was about 18 months or so. The only problem was he was the only of his species. When I finally got around to adding 3 WC females, he killed them all.
I have four females that have all bred at about 3 inches. The males were over 5 inches but I think the smaller ones would start around the same size if given the opportunity. They would hold thirty or so fry. Now at 4+ inches they hold more like sixty. There were some false starts where the eggs were being held and then nothing came of it. Don't know if this is caused by inexperience or what.