How old are rabbits before they can start breeding ?

I don't want to breed them. i have two rabbits ( both female i'm told) but they are only 9 weeks old just left their mother i have had them for a few days. and the smaller one is chasing the other around ( I have another question on here) it doesn't seem aggressive as they make no noises and they still huddle together and sleep close to each other. anyway someone mentioned that one could be a boy ... so how old before they can mate ? and have babies ?