I tried to wait with Bo - I really did. His EB specialized vet --- the gal the rescue uses -- said to wait until at least 9 months but "wait as long as you can stand it". And I quote. Bo was done at 6 months. He appears none the worse for wear and gets bigger and thicker every day. The vet seemed to believe that his size at adulthood would be impacted if neutered early. He's two this month. He's well over 75 lbs.
I think the longer you wait the harder the surgery is on the dog. (that's my opinion; I have no facts to back that up)
I had Bo neutered at my vet and my expense -- even tho the rescue would have paid for it. Using a doctor you know and love and knows EBs....would be good for your peace of mind.