This is a personal preference. Some do it when they are younger versus older and vice versa. There are pros and cons to each side. I always go younger, the main thing being the amount of pain and cancer. I had one dog(my sisters) that was about two when she was fixed. It was awful, she couldn't walk and she cried. At the same time my own 6 month old puppy was fixed and running circles around the older one. My GSD puppy was about 5 months when she was fixed. No signs of pain or discomfort, she has grown upwards and now at 14 months she is starting to fill out. Her body did was it was suppose to, per the vet. If you can wait and you feel comfortable with that, then that is fine too.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD