sleep training question/opinion

I'm going back to work in two weeks. My 7 week old has shown some signs that he might be ready to sleep train (falling asleep away from me in his rock n play, sleeping for up to 4 hours uninterrupted).  I've read conflicting information about sleep training, some say if you wait until they're 8 weeks it's too late for forever, others say they're not developmentally ready until 4 months. He also co-sleeps with me and I want to either transition him to sleep in his rock n play (at this point this would just be used as a stepping stone to develop a routine) or right to his crib. So is 8 weeks too soon to sleep train him? If you have sleep train this young what method did you use?