We did an experiment and loaded a bin with 200 adult females and 30 or so adult males. It's been almost three months and the babies are just over the 1/2" mark. They do take time to grow, but once you have another generation reproducing, you're on your way.
how many adult pairs do you have? what are you keeping them in? what are you feeding them? are you supplying water crystals?
what are you using for your heat source?
are you providing complete darkness ?