I always like to see people wait til a dog is at least a year old. What I like is that it gives the growth plates time to close. This can be a little trouble if you have a girl because it means you have to take her through at least 1 season, sometimes a challenge if you have not had much experience with doing it.

I know the vets push hard for earlierlier spay/neuter, but I think you need to see both sides of the coin. Here is a link for some reading about just that question. http://www.roycroftcavaliers.com/Early%20spay%20neuter%20article.htm