How long from born to be able to breed?

[SlitherinSisters]

Well there is sexually mature and than there is optimal for breeding.

By age 5 weeks rats are sexually mature.

The optimal breeding weight for females is around 250 grams, I really don't go by age I simply start pairing them when they reach that weight, takes a while to reach that weight but definitely not 4 to 5 months , usually by 2 months old the females have reach 250 grams.

Males well you have to use common sense at 5 weeks they are ready however if the size difference between the male and the female is too big the male is just gonna get beat up.

Mine are usually breedable at 2 months or so also, I don't keep track of age either. I pretty much go by: once they hit the size they can't be eaten by my 1000 grams and under, then they are breeders So that puts them at about 3+ months old when they have their first litter. 4-5 months would be almost full grown. They can start breeding around small/medium size depending on your definitions.