We started training at home when Toa was only 8 weeks old and he picked it up really quick. I think the best window is up to 4 months-- not to say you can't train after that-- but it's when you have the best attention span.
The only thing I would be concerned about is that you really shouldn't work a large breed pup too much because it puts a lot of stress on their growing bodies.... so maybe keep the sessions short at first.
Good luck, it sounds like you're in for some great fun!
