I too have read that. But I believe that is in reference to females. I have heard that male rats can hit maturity within 2 weeks of being born. But that could be way off... so could someone back that up if it is correct?
-Kyle
Green = 8 Ball Python
1.3 Normal Ball
1.1 Nerd Lemon Pastel & VPI Pastel
1.1 100% Het Albino and Homo Albino
1.1 100% Het Butterscotch/Yellow Hypo
0.1 Kenyan Sand Boa
I like to start my female rats breeding around 4.5 months which is generally about 250 grams. This allows them to be of good size to successfully carry, birth and raise a nice feeder litter for you. As far as males I like to get a bit of size on them as well just because the poor things tend to get kicked off when they get all "friendly" with some of my big, experienced female breeder rats LOL. They don't have to be big big, just a decent size really. Do watch buying a really big male from a pet store. Some of them are old retired breeder males and may not be as highly fertile as you want in your colony male. Male rats are sexually active by 5 weeks of age so you want to get them weaned and seperated by gender by that point or they will be chasing their female litter mates and wasting your food dollars on that instead of growing into chubby feeders.
Other than a nice healthy rat when it comes to males, go for nice temperment both with you and with the females. Some males are overly aggressive breeders and will be rough on the females. Also you don't want a bad tempered male rat, they get big and they bite HARD....also rat temperment is genetic so good temper in both parents makes your life easier when you reach into those feeder/breeder bins.