Originally Posted by DaveA:
My "one size fits all" answer is 12-15 months. Honestly it depends on the child. When I think they are ready to lay still on a cot I switch them. Or when they get to the point they can escape the pack and play. 
Same here.
I've had kids more than ready to be on a mat/cot before 12 months but licensing requires a crib or PNP until the day of their first birthday.
I've also had kids that could/would have stayed in a crib or PNP long after they turned 1 so it really does depend on the child but my goal is 12 months.