I'm going to copy and paste something from a pei forum because ti says my stance pretty good,but I'll answer the other stuff too.
There are a lot of things that go inot it. Because I never trust that a person can keep a dog without making more I usually say neuter as soon as possible,BUT I would never alter one of mine before they have fully grown. For my dobe that may be as old as two. Some people also can nto deal with a female going through heat,or a male when they smell a female going through heat [Bang Head] Its not fun stuff!
If a dog has a genetic pre disposition to have bad joints,bones,urinary problems etc,it is better to let them get all their growth hormone that goes along with the sex hormones. A dog that is fixed before puberty grows diffrently. They are a little taller and their bones(from what I understand the sex hormone should eventually seal off the growth hormone and it doesn't) grow diffrently.
But to the normal pet owner who doens't have a ton of experience I would say to neuter as soon as possible,same with anyone who has had an accidnet in their home. And I don;t care how old a rescue in my house is,they will be fixed during their transistion to their new home.
This is a huge issue with dobes and now labs with the recent study on hip dysplasia. I will try to look for the articles.
This is one I found and the other discussion was on a dobe board you would ahve to join to view but I'll have to look for it.
http://www.caninesports.com/SpayNeuter.html
This si a great quote form the article" I think it is important, therefore, that we assess each situation individually. If a pet dog is going to live with an intelligent, well-informed family that understands the problem of pet overpopulation and can be trusted to keep their dogs under their control at all times and to not breed them, I do not recommend spaying or neutering before 14 months of age."
I hate saying stuff like this because then there is more of a risk people will have accidnet pups but when I weigh the pros and cons early altering just isn't for me. But it is for a lot of people.
Found the other links! you may have to join but its worth it.
http://www.network54.com/Forum/11341/thread/1130246256/
That rally answered everything but will you get your dobe altered. byron is six-ish now and still not done. He had a reaction getting a lump off and I've not wanted to put him back under. My corgi recently had a tumor and got fixed but it came back that she would ahve had the tumor regardless. I don;t know if I mentioned it above but the inverted vulva(is that what they call it?) seems to be pretty common in dobes and if you fix before the first heat it will not fix itself and often the dog is fixed before its even noticed.