I have a little guy who can fully immerse himself in stories and fantasy plans... and who can talk your ear off.
You can give good boundaries without trying to control him. You can tell him that "the kitchen is going to be a quiet zone for the next five minutes. I'm going to set a timer, if you need to talk, go talk to your toys" and then be silent. If he starts talking, just take him by the hand and walk him to his room. You can even whisper "talk to you later, it's mommy's quiet time" and walk away.
Here's something funny-- we've gone through several of these phases of interest. When he was three-- four, it was big machines and welding and pumps/fountains. He could tell you all about them. Four and five -- dinosaurs. Knew name after name of the dinos? Guess how many he's remembered now that he's nearly 8? I just capitalized on these moments, brought in lots of books and experiences and tried to engage on his level. Now it's creepy stuff and pretend superheroes he's made up, and he has elaborate stories. I encourage him to draw these ideas, to build them with Legos (the ultimate obsession, Legos!), to write them down.
All kids will have their own proclivities. Many grow out of their sensitivities. Two years ago, hair washing was a battle, as were baths/showers. Now it's no problem and he loves a nice hot shower. We've taught him that total strangers are out and about to do their own thing and we don't just tell them whatever is in our heads. "You can say hello (because he's a friendly kid) and then let them walk on. If they stop to talk to you, fine. Otherwise, they are here to do XYZ just like everyone else." We just continue to teach him those life skills of what's publicly appropriate, but at four, he wasn't really 'there' yet.
You will have to give him guidance. L.. It is exhausting. Contact a family counselor if everyone in your family is feeling it as deeply as you describe, because there may be another dynamic going on which you aren't aware of, I don't know. But it is okay to take the little chatterbox to his room when you are trying to make dinner and can't think for all the noise. He has to be taught how to be considerate of others. If you think there is something else at play, then please, talk to your pediatrician and ask about a referral to whatever specialist they feel is necessary. I think we'd all be remiss to suggest that there's anything 'wrong' with your son from the information you gave.... he could be just really immature and active. But I would start with making some structure and boundaries. You might even use a timer at the dinner table so that he can talk for five minutes about his stories/desires and then it is time for him to listen, to learn, and to be guided. "Oh, remember Billy, we are talking about the ball game Daddy went to last night. You may ask him a question about the game or talk about that-- that's our conversation right now." Make it simple and bring it down to his level-- it sounds like he's the only little one in the family right now. Be sure you aren't making him the star of the show, too, by constantly addressing him. You can also decide as a group that if he keeps going back to his conversation during other topics that you all just ignore him and if he protest, a quick "oh, we're talking about Sally's music class now" and move on.
ETA: if you are still stuck like this after creating structure and giving guidance, yes, there may be something which is organic to him and not parenting-related. My guy has some profound attention issues and we have had to figure out how to parent *him* as opposed to a neuro-typical child. It's a balance, but we didn't automatically come to the conclusion that it was him-- we did a lot of things to provide structure before finally deciding that we needed someone specializing in attention issues. In a lot of ways I am glad I waited until he was old enough for this to be a certain conclusion than a suspicion. I'm not sure things would have been any different for us had he been diagnosed at 5 instead of nearly 8 and that he has more awareness of his own self. Sorry this was so long...