Training age

How old must a puppy be before you can begin teaching him commands like "sit" or "stay" etc? When they're still very young, they really don't care about letting you get away from them and I'm wondering if one should wait till they're more mature before trying to teach them certain commands.

You can start teaching them at any point. The earlier the better. Granted, if you have a newborn puppy it's not going to work trying to teach it sit or something, but even in the first few days of life Early Neurological Stimulation is very beneficial.