what is the earliest age you can have a dog neutered at and is is a good idea

The Guide Dogs have found that around 10 months is about the best.

It can be done as early as 6 months if unwanted behaviour problems arise or become an issue. We recommend them being castrated at around 11 months at the vet practice i work in.

Sue

I would prefer not to neuter until the dog was at least 18 months old unless there were overwhelming reasons to do it earlier.

Maybe this wil help:

http://www.gsdhelpline.com/castration.htm

I agree with Tohme.  A dog needs the testosterone created in the testicles to fully mature, in my opinion.

If it were me I would wait until the dog has matured physically and mentally.... :-)

Me too :)