Originally Posted by comyncats

Whether they're in a cage or free in the house makes no difference - once their hormones kick in, you could have a pregnancy, though probably not for a while. Females can come into season from about 3.5 mths (in extreme cases - I once had a burmese who was calling at 4 mths) and a male can be sexually active at about 6 mths (also an extreme).

I suggest that you neuter both of them before too long.

A female cat needs to be fully grown before mating, which means about 10 - 12 mths, usually.