What age can you start training a dog basic commands?

Nine weeks is fine to start training, but he is still young so he will probaly try to bit you but i find this way helps... get a treat and put it about 2 inc away from his face then slowly (not too slowly) lift it up and behind him then he fill follow it with his eyes and sit, straight away when hes sat give him the treat and praise him. Keep doing this and he should get the hang of it. But remember its still early days so dont worry if hes not responding right away.