Opinions vary about what age is best. I've had/have lots of dogs over the years and have always had mine spayed or neutered by 6 months of age. Some people prefer to wait a little longer thinking it is better for joint health etc. but of the 9 dogs I have now all have healthy joints and 7 are athletes that run about 250-300 miles per season (how many miles depends on the dog and which team they're running on).
Beware of Mushers...They will suck you into their addiction!
If your dog thinks you're the best, don't seek a second opinion!