It is ultimately your decision, and while people's opinion on this vary widely as you can see, the age that Douglas has attained falls somewhere in the middle range. He is about six months old, if I understand correctly and while many suggest that one try to wait that full year (at least), it isn't always possible.
Personally, I think to neuter UNDER the age of six months is not good, for all the reasons "Deerie Me" mentioned, and then some. I tried to wait until both Oliver and Henry had attained the age of one year, but Oliver started marking at 8 months, so that was it for him. Henry did much the same, only I think he was about 9 months. They both filled out nicely and continue to fill out nicely.
Talk to your Vet and learn what you can, as neutering will not be the ultimate solution to behavioural issues. You may wish to contact a trainer once he has healed, and do some one on one work with him while he is still young. Your Vet should have some answers, and some suggestions.
Best of luck to you and especially Douglas!
Do keep us posted!