I’m on the fence on the subject. Though it can increase territorial aggression and wanting to wander when there’s a bitch in heat around, it will not actually change the dog’s personality. That’s a myth. There are pros and cons to the operation; make sure you read up on both.
For age, it depends. I’ve heard that spaying/neutering early can effect the growth of the dog, especially in giant breeds. They don’t get all the hormones that they need to develop muscle mass and the like.
It also depends on what you want to do with your dog. If your plan to show him in UKC events or the like, he cannot be neutered. But if he’s just a pet, then it’s probably the best choice.
However. I do feel that responsible people can keep intact pets. Dandi is not spayed and will not be until she’s a year or two older. As long as you keep track of heat cycles (if applicable), keep track of who your dog is playing with and keep it confined and leashed, there’s really no way for it to run off and have babies.