2-3 weeks is way too early for rats to be weaned. 5-6 weeks of age at removal from the dam is recommended. I pull males at 5 weeks, and leave females in with the dam until it's time to breed her again. 2-3 weeks is when their eyes first open, not when they become sexually mature. They haven't even started eating solid food, really for another week or so, and then it's a supplement to milk.
It's hard to tell the gender with those pictures, for me. General rule of thumb - if there's a bare strip between the anus and the clitoris, it's female. If there's hair between the anus and the penis, it's male. Males and females will need to be separate, after 5 weeks of age, but make sure that you have at least two of each together. Rats are social animals. They need at least one other rat in with them for company.
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