5 month old female has started growling at her brother?

[Alekto]

Hi Alekto, no they haven't been spayed or neutered yet, the vet wants to do this at 6 months ...... so 1 more month (and counting)! As for Cesar being a coward, I would never suggest that. As I said, he is my brave boy - but I know many a brave man who has backed down from a hormonal female in order to live to fight another day :-)

I'm no vet, and no expert, but to me her reaction would mean it might be more or less time now for Mandy at least? may be you might check again with your vet, see if he would do them a little bit earlier just in case? it's just that kitties don't really know that brotherly love isn't "really a done thing you know"... I mean may be your vet wasn't really planning on little Mandy being rather precocious, that's why he set the 6 months date? on the other hand Mandy is just growling, not calling, so just hormonal but not in heat - and Cesar seems to not really be interested if he's backing away.... so I don't know
Jacki, please impart your wisdom :-)