As shocking at it is, many vets are starting to spay and neuter pets as early as 8 weeks of age. Most vets will tell you to get have the surgery performed before 6 months! We have always recommended that people delay this in females until they have gone through at least one heat cycle (usually happens between 9 months to a year) and for males to delay to 2 years of age if possible. There are many reasons we suggest this, not limited to increased rate of orthopedic problems including hip dysplasia, increased risk of torn cruciate (in the knee, usually requires surgery to repair) and increased risk of cancer just to name a few. Here is an excellent article where Goldens were studied and the increased health effects were notable.
So what do you do when your vet is trying to pressure you, or even scare you into thinking that you need to get this done by 6 months? Simply inform them that you have done the research and want to do what is best and healthiest for your dogs life and longevity and that you will not do it until you are ready to do so. Your male dogs will not try to breed everything in sight and will not become aggressive or dominate being intact until they have reached full maturity. Your female will not become pregnant to a litter of unwanted puppies if you keep her in your yard during her heat cycle. We also suggest that you only leave them out when you are with them and they will still be healthy and fit if they don't go on walks in the park or around the neighborhood while in heat. If they tend to drip or leave blood droplets from their heat cycle around the house, then go to any pet store and get a pair of "Bitches Britches" or one of them kinds of doggie diapers they sell for such an event.
Just by delaying this one surgery, your dog will be healthier, will potentially live a much longer life and you will be saving a lot of money at the vets when you are not dealing with the effects later down the road of early spay/neuter.