Co-ed older rats

Question
Hello Ms. Todd,
My wife and I had a litter of rats just about 3 years ago. Only 2 are left, a brother and sister. They have been removed from their large, many leveled cages as they are not so agile anymore and each put in a smaller cage. We recently started taking them out to play together and they show no signs of aggression or hanky panky toward one another. The girl just grooms the boy a bit and they wander a little, but for the most part just sit together. Do you see any reason they could not be housed together or should we just leave them in separate cages? Just don't want the much smaller female to get hurt if the boy suddenly feels young again.

Answer
No do not let them near each other unless you want a litter of rats and not to mention that having a litter of rats at her age could kill her.  Now there is a good chance she has gone through menopause, but I have seen people assume this, put them together (older males and females) and before you know it, the elderly female is pregnant. Males are fertile throughout their life and females "usually" are through menopause around 2 or so but its not a guarantee.  If you want to let them wander around together supervised, I dont see it being a problem...you can even have her tested to see if she is still fertile (blood test) but just watch them carefully while out playing. I would not let them live together though.  Wish I could say yes, but my semi-professional opinion would be to be more cautious and not put them in same cage where they could nest and mate.