Newt

With the small constrictors of that group I would use the rough age of 1.5 - 2 years for males and 3 years for females. From 2 - 3 years of age the rosy boas will start to put on adult weight and female should be allowed to do this in order for you to keep them healthy and breeding a long time. Rosy boas are also in most repects handled and breed the same way kings and corns are breed. You will need to give them a slight brumation period and that will help alot in breeding. That is why I say give them a little more time to put on weight so they can go through that with no ill effects. These are just suggestions and dont have to be followed to a tee but should work well for you.

Thanks,
Chris