The size of fish isn't always a perfect correlation to age or sexual maturity. If they were kept in a tank with lots of water changes and frequent feedings they might be a pretty decent size but still be too young to breed. I believe that my Ruby Greens started breeding when the females were around 1 1/4" to 1 1/2" long. The males are usually a bit larger than the females and my males also grew larger more quickly.
Several females did not hold to term the first and maybe even the second time they bred. But once they get the hang of this mom thing, they are really quite prolific.