I know this is a little late in the thread, but as i am myself due to get kittens, a number of volunteers for cat protection have told me (and others who rescue kittens) never to let a kitten outside until they are at least 12 months, as they have no road sense and they could end up getting killed, and as others have posted, if they are not neutered then it would not be fair to the queen if she gets pregnant at a young age.

Emma x