Our 14 month old female cat plays for hours with our neighbours 2 year old Tom (Monty)
We brought a kitten home in June (same Mum) and she absolutely hated him on sight which ended in us later having to rehome him (good friend has him and both are very happy!)
So she wouldn't accept the kitten but loves Monty and doesn't bother at all if he wanders into our house. He is he only cat she seems at ease with. If another cat comes into our garden she goes mad. Anyone else's cat have a BFF?