I've never one time, on this site, contradicted anything a vet said, but that's the first time I've ever heard a vet say to wait 6 months. I've had 3 males neutered but I had one of mine done at 16 weeks because he had a bald spot and was sexually developing...meaning, he could father a joey. I didn't want to separate him from everyone else. He was very bonded to them and I wasn't going to do that to him. I had another done at 12 weeks as have many, many others. I did that because I refused to separate him from his colony as well but also didn't want to chance inbreeding. I highly recommend calling your own vet and asking. I personally think waiting until 6 months is irresponsible-especially if he becomes a dad. No one has to get all up in arms because I don't agree. No, I'm not a vet but have been around here long enough to KNOW that that is not common practice. If he did happen to become sexually mature before the neuter, it will be their mother's joey(s) and that in itself is a whole separate world of problems.