If you are planning on allowing your cats outside, I think 12 months is ott, most people let them out after they have been neutered/spayed at about 5/6 months, and I see nothing wrong with this.

Health wise, you can let them out once they have had their injections, but a femal could obviously get pregnant if allowed out before she is spayed. Also if they are too small, they can be attacked by magpies, most cats are big enough not to be attacked by about 3 months old.

You could of course take them out on a lead and harness before they have been spayed, this will help them get used to be out, but will mean they can't get into any trouble while they are little.

But remember, if you are getting kittens at the moment, we are going into winter, so its not the ideal time to start letting cats out. And if you let your cats out, you should always provide them with some sort of inlet into the house (cat flap) or shelter in another building (shed).