Check out the Stingray section.. lots of Motoro breeders. Takes 2-3 years for maturity, they can reproduce at around the 12-14" range, sometimes smaller but less likely. Age has more to do with size when it comes to maturity. They don't eat their own 'pups' usually, unless they are huge, hungry, and you don't separate or notice the 'pups' right away.. some people have success leaving the pups in with the parents - other people have the pups get chewed on.
Try using the search function you will find hundreds of posts about breeding Motoros they are the most commonly bred stingray.