there's mixed sentiments on when to separate the genders. the facts are that the males are starting to become sexually mature at 4 weeks and that the females can get pregnant at 5 weeks. but it is reported that the males won't be mentally there until 6 weeks though there are always bound to be the overachievers. by 4 weeks the babies are able to eat solid foods and strictly speaking no longer need mother's milk (in my experience the mothers were no longer nursing by then either). so rat babies can be separated anywhere between 4-6 weeks and anything after that is REALLY asking for trouble. however at 4 weeks the males still should have an adult rat to be with to teach them how to be rats, socailize them. so some people give the boys until they're 5 weeks but if you do have an overacheiver in there he could get mom pregnant, so there is that risk. what i did to prevent this and not to harm the babies social upbringing was to borrow an "uncle" for the boys to be with until they got a bit bigger and separated everyone at 4 weeks. it worked great too and "uncle" Tsume loved the little ones and they him. when they were grown other then a few of Snicketts (who had temperment issues of her own which i believe were passed on to some of her babies) they all grew to be well mannered and behaved little men.