my kittens are coming up to 5 months they are brother and sister, ive booked them both in to be done next week but i feel the female is still to little to be done, im thinking i might hang on till october (she will be kept in) do you think this would be ok?
Only provided you keep her indoors all the time - if she is allowed out she will more than likely end up pregnant.
Size is not such a consideration as age, and at five months I would consider her to be old enough. Far safer to have her spayed at five months, than to risk a a pregnancy at six or seven months.
I had my female cat 'seen to' at 5 months, and she was tiny (she comes from a small breed). It did her no harm, and she has grown to a very healthy and active cat. Still small, but cute and mad. Check with your vet - see what he / she thinks.