True about neuter/spay a MC cat...

I know that question is older and many times people asked before but I'm in troubles with my 2 MC kittens (Baloo and BlueBelle whose are brother and sister) so I re-post the question hoping to have some more suggestions or infos about...
Is true that neuter / spay a MC cat reduce his/her possibility to became bigger? I mean "bigger" as everyone dream that his/her MC will be according with breed standards.
The breeder of my cats suggested me to do that only after one year of age but I would like to avoid the possibility that something will happen between brother and sister during next months...
About fact that Baloo (male) could start to spray around the breeder said me that anyone of her male kittens did that at now (they didn't showed that kind of behavior in the past) and so she is confident that will be the same for Baloo, about time in which BlueBelle will be fertile she said that usually that happen at 10 months of age or later.
What do you think about question? Any suggest for me? An now Baloo is about 4 kg of weight and BlueBelle is lightest, only 2,6 / 2,8 Kg so I guess that Baloo is the cat with mayor possibility to became "bigger"!
Thanks for reading and replies...

Our was neutered at 8 months, he didn't change at all: very active and chasing the intruders.
And he is now very big and slender.
http://i144.photobucket.com/albums/r.../Photo2885.jpg
our 30 kilo chow along the "little" MC

Our breeder said to get ours neutered at 8 months. The theory is that, as they are a slow-maturing breed, you can leave it a bit later than with other breeds. Also, the longer you leave it, the more chance they have to grow bigger. However, many MCs who are neutered at 6 months, or even earlier, ie, before they leave the breeder, are still huge. So I would not worry about the neutering affecting their growth at all.

I think the important thing with neutering is to get it done before they start to get 'the urge' and spray around the house or behave aggressively to other cats. The trouble is, each cat may reach this stage at a different time. We had Larry and Monty done at 8 months, which is exactly what our breeder recommended. I should probably have done it sooner as Larry had started to wee on the floor. Herbie matured a lot quicker and his behaviour changed at 6 months which rather caught me out. Then I was away for a week so he was eventually 'done' probably 2 weeks too late. He was so big by then that the vet had more than enough material to work with, so to speak. This was back in February and for months afterwards Herbie would wee on a certain area of floor, any chance he could get. It's only now that we have started to relax about it and can more or less trust him not to do it.

According to my experience, 10 months does sound rather late and I would certainly get it done sooner. If you think your boy is ready, then get his sister done at the same time, so that they go through the experience together.

Mine got done at 2 years old - I don't know about the size issue, but I am regretting very much leaving it so late for other reasons. Apparently if you leave it till they mature then the body's reaction has a chance to be stronger. Mine is currently going through said reaction and it ain't pretty.
Being a first time MC-Humanz, I can't talk with experience about the breed, but I was told (by my breeder, who really wanted me to spay Neevie - so that's to be taken with a pinch of salt) that she actually would have a better chance to get bigger if I spay her. It's too soon to tell yet if that's true.

Thanks to all for suggestions and info. Maybe I will try to wait a little bit more paying attention to Baloo's behavior and his urine smell! At now, after yours feedback, I believe that wait one year of age is not useful, I guess the right one age is 7/8 months also because I've read that cat's body react better to the treatment when cat is younger... Next week I will meet the vet and I will ask to her as we can agree for the job, basically if Baloo will start to spray I will need to do it as soon as will be possible! I think also that could be a good idea do the work on both cats so they will recover from treatment together. In event of news I will tell you them!

That is very sensible, as you also don't want to risk a chance mating. The cats don't know they shouldn't, and even if you think yours are not mature enough, you could be surprised 9 weeks later and that's not good. Spraying is not really a problem at this young age, in my experience, but watch out for a change in urine odour and get your boy to the vets straight away if you notice it. In your situation, I would suggest that 7 months is a good time for neutering, I don't think delaying any longer will make a difference to their adult size.

Hi ale.agos, if it were me I would get both cats neutered sooner rather than later. I have had three maincoons, two of which were neutered at 12 weeks old, one male and one female and both these cats were enormous. My other boy Oscar was neutered later (6.5 months) and he is the smallest of the three. It is becoming more common in the UK for breeders to neuter kittens before moving to their new homes as this prevents irresponsible breeding. In your case it is really important that your cats don't mate due to then being siblings. As musicalife has said, Baloo and Bluebelle don't know they shouldn't mate and while Bluebelle may not be sexually mature for some time yet, do you really want to take the chance? Yes maine coons are slower to mature, but there are individual differences and she could well be able to become pregnant at only 5.5 months.
As for males spraying, I believe that once they start this behaviour, it can be really difficult to stop. The choice is yours but I would rather have two healthy happy cats than risk pregnancy. And as I have said, my experience suggests that neutering early does nothing to limit growth; if anything, it can make them bigger as they spend longer in the juvenile state where rapid bone growth occurs.