Hello, I understand that sometimes it can be a bit irritating to have a "chatty" cat. Some breeds, especially the oriental types such as Siamese cats, are more talkative then others. They seem to be born that way. It also seems that kittens and older cats seem to be chattier then adult or middle aged cats.
If you want him to talk less you need to ignore him when he talks. The more attention and treats he gets when he talks, the more likely he will be to talk more as he has been successful getting what he wants that way. Expect him to get worse before he gets better as this has been the way to get what he wanted previously.
Best of luck with your fellow, please let me know if you have any further questions.