6 months is the general time frame when it comes to neutering, however it differs for everyone. Some prefer to wait until their males are fully matured, some like to get puppies over 3lbs before being put under, etc. I think 6-8 months is a good time. If a dog is beginning to mark alot, then do it asap to break the habit as quickly as possible. Jackson had only lifted his leg one time on my dads screenedin porch furniture at 6 months old and a month later he was neutered!
Never marked indoors ever since. Neutering CAN calm them down but it shouldn't change their personality at all. Jackson was almost 7 months when neutered and he is still at 1.5yrs old his same goofy self.