Socializing female rats

Question
Hello! This may be a silly question, but: currently we have one approximately 1 1/2 year old female, she is very affectionate and very energetic. We would like to get her a companion, but don't know if she would get along well with a new rat - I've tried introducing her to another female before (same age), but they never got along (however, the other female was a rescued rat from an abused home, and a biter, so not the friendliest one in the bunch). Would it be better to find a 6 week old female, or one a little older?

Thank you very much!
A  

Answer
Absolutely go with a baby. Introduce them on neutral terms, in a clean area that doesn't smell like either rat; and go from there. A baby is naturally submissive, so you shouldn't have a problem with your doe feeling threatened. Once they seem to be getting along well, you can transfer them to a clean, rearranged cage and see how they do. Good luck!