This is not, IMO, a topic about aggression or marking. Yes, if your dog is aggressive, neutering might be something to consider as part of the solution, but it's not a solution by itself. For what it's worth, my intact male at 8 years old still rarely lifts his leg (and he's been bred). My three year old neutered dog marks everything. If you talk to enough people you can find every permutation.
Early neutering is for me, a health issue. Now, first and foremost if you can't control your dog and keep him from breeding, then neuter as soon as you can. But if you can and are willing to guarantee a dog will never be bred accidently, I am a firm believer in waiting until at least two years old.
Here's why: Nature gave dogs hormones for more reasons than breeding. They are used to help a dog grow and mature the way he's supposed to. Dogs (especially males) neutered young do tend to grow taller and lankier than males allowed to grow naturally. I've seen it over and over, especially with males. I can pick them out usually. In addition to growing taller and thiner, this leads to increase risk of things like ACL and CCL tears. I know many people who have had soft tissue injuries on dogs neutered young. Of course it happens on intact dogs too, but I find there is an increased risk with early spay/neuter.
I will also add that the earlier you spay/neuter, the bigger an issue this is. If someone wants to neuter at a year (as opposed to the two years I prefer) I don't think that makes much of a difference. If someone neuters at 8 weeks (yes people do) as opposed to 2 years, the difference is much bigger.
The following article has probably been posted many times but it's one I find to be accurate in terms of what I observe: Canine Sports Productions: Early Spay-Neuter Considerations for the Canine Athlete
I should add that for my personal dogs, I have decided I will never neuter another male unless I have a medical reason to do so. What my dog went through when he was neutered was not worth it to me.