tofu pup
Moderator
We've had intact adult males who mark (ugggh), and adult males who would be mortified to lift their legs in the house. It seems to be a function of temperament and self confidence; I don't know if age at neutering has a huge effect (which is to say, you may have a polite, gentlemanly dog, even if you wait to neuter).
As to coat... I hate to break it to you, but the coat changes regardless of when the dog is altered. It doesn't matter if they're neutered at six months or six years.
As a show person, yes, I'm partial to the "true", hard coat that comes with intact hormones and sleeping in the cold. But I encourage you not to worry about it too much; you will see here on the forum that there are many neutered males who sleep inside and have perfectly-lovely coats.
Personally, I'd think towards letting a dog or bitch have all their parts for as long as possible. They evolved to develop with hormones; why upset the cart too soon? If there are behavior problems, of course get them done, but otherwise, let them finish growing if you can. I'd lean towards eighteen months or two years - they really aren't quite grownups yet, at a year.
As to coat... I hate to break it to you, but the coat changes regardless of when the dog is altered. It doesn't matter if they're neutered at six months or six years.
As a show person, yes, I'm partial to the "true", hard coat that comes with intact hormones and sleeping in the cold. But I encourage you not to worry about it too much; you will see here on the forum that there are many neutered males who sleep inside and have perfectly-lovely coats.
Personally, I'd think towards letting a dog or bitch have all their parts for as long as possible. They evolved to develop with hormones; why upset the cart too soon? If there are behavior problems, of course get them done, but otherwise, let them finish growing if you can. I'd lean towards eighteen months or two years - they really aren't quite grownups yet, at a year.

-- and keeping an open mind on the neuter part.