When we were deciding on neutering Dozer or not (French mastiff) this question weighed on my mind. Through all the research I did, I found the best idea was to wait until at least 12 months. Giant breeds usually don't finish growing/maturing until well after 24 months and fixing can lead to growth problems. We're not fixing him, but he's just now hitting the point where we'd get him fixed, if we were going to. He's 2 1/2 years old and is JUST NOW finishing growing. Have you talked to your vet about it?