not necessarily true....
and never seen a 5 week old rat breed in 16 years of my experience breeding rats.
My offspring are removed once their eyes open and either are sold or they go to a community trough where they last maybe a week until the next orders come in....
In the past I have sat on a trough with a mix of rats from 5-10 weeks old over 2 months and no litters. At 8-10 weeks I normally start freezing....prices between medium and large is not big enough to keep feeding them but the difference in food consumption is obvious.