But if he's not castrated until he's 12-18mths, will I have to be extra careful around the bitches that he'll be playing with (his mum, his sister etc)?

Yes, you will have to be super careful when ther are in-season bitches in his vicinity Is there any reason why your bitches are not spayed (if they are indeed actually yours)? Simply do not allow him anywhere near any in-season bitch.

Well yes, of course, in just the same way as you would make sure you shut the door so he can't run into the street. You will have to keep them apart and if needed by putting either the bitch or the dog into kennels for a couple of weeks. I am not saying you will not find a vet who will not castrate at an early age, some seem to wish to do it as soon as they are weaned, but just that IMO it is not a good idea as far as the dogs well being is concerned, others will have the exact opposing views.

Wonder why you got a dog when you knew he was going to come into contact with intact females, you must have either thought you would be able to cope or that you would have him or the bitches spayed, what ever you decided before you got him why have you changed your mind or had it changed for your, is it just that you thought the dog would not be fertile until he was older?

Im going to answer for Shelley, because I think your reply is a bit harsh. You are implying she has no diea what she's doing, also that he will be around the other dogs all the time.
He won't be in contact with females all the time.
The breeder of the dogs is my sisters friend, and they spend time together (going camping, to each others house etc).

She knows they will have to be kept apart when the bitches are in season, but she just didn't know from what age a dog will be fertile, so when to keep them apart, and she also didn't know the best age to have a dog castrated - hence her asking the questions.

She has actually said in other posts on this site that she has no dogs yet, the bitches aren't hers etc

Did not mean to sound or be harsh, was puzzled as to what had changed to bring this problem since the decision to have a dog rather than a bitch. I was replying to this comment

"But if he's not castrated until he's 12-18mths, will I have to be extra careful around the bitches that he'll be playing with (his mum, his sister etc)?

The answer to that is yes you will.

I don't know why they decided to get a dog....although i'm glad, as Teagan plays with dogs better than bitches!
They haven't even got him home yet, he's too young

Sorry but I have to disagree with a lot of whats been said. Six to eight months is imo about the right time to neuter a dog. A male dog has all his male hormones right from being in the womb and its a good idea, if he isn't to be used for breeding, to get his bits removed before he starts displaying adolescent behaviour. Why go through the difficulties of an adolescent male, then get him done afterwards.

A bitch is different - she doesn't possess female hormones until after her first season and imo shouldn't be spayed until after this time.

Dare say there will be loads of you that disagree but I see enough adolescent males in my training classes to know those that are castrated before this time make much better pets.

Get him 'done' before he gets any ideas!

I have a friend that has 4 un-neutered dogs, and they are fabulous pets, rarely a cross bark between them.

As for the humping, my MIL's dog is neutered, but he still does it..............my Rosie was spayed last March and she still humps her daughter.....lol.

Some males do 'cope' very well un-neutered and are never a problem - but lots are. If you've got the added temptation of bitches in the house though it is best to get them done.

I was told by my vet, that if a dog could produce already at 3-4 months.. Of course he wouldnt really know how or where though

I was dogsitting a rottie boy and at the time Luna hadnt been in season, so I just asked the vet, just incase..