Best time to neuter Aussie

Question
I own an 8.5 month old Aussie male.  He comes from old-school working bloodlines.  I don't intend to breed him and was wondering when is the best time to neuter?  He started lifting his leg on things a month ago and even peed on another dog at the dog park the other day.  When is the best time to get him neutered?  My breeder originally suggested I wait until he is 12 to 16 months old in order for him to "grow out correctly", but he has already started showing signs of maturity including lifting his leg to pee, humping (only at the dog park), and pretty aggressive play at the dog park as well.

Answer
The main reason for allowing a dog to "grow out" is if you are going to show.  Generally speaking, a dog reaches their mature height and structure at puberty, and they fill out a bit later.  But, in pet dogs, I usually advise neutering before the leg lifting begins, because some dogs don't quit after they are neutered.  (Although, don't assume anything, because dogs generally need time for the testosterone to completely leave.)
My male dogs are usually neutered by the time they are 6-7 months of age, so I would say that if you are comfortable with doing it, and your vet is ok with performing the procedure, go for it.
I certainly do not think that he should be at a dog park by the time he is age 12-16 months if not neutered, as some dogs will take exception to his status, even if they are neutered, and you could have a dog fight on your hands.