Totally not a judgment, but I don't understand how anyone can cosleep. I can't sleep with my kids in my bed. They move so much!! We went on vacation a couple of months ago, and DD1 slept in a king with us, and she started out with her head on the pillow in between us. Fast forward about ten minutes, and I was getting kicked in the face and her head was at the foot of the bed.
To answer your question, I say the earlier you get LO in a crib the better. Too many of my friends still have their two to seven (!) year olds sleeping in their beds with them. Better to break them of it now, regardless of the crying. GL ;)