Here’s a list of concrete reasons why we recommend rear-facing past age 1 and 20 lbs. That old recommendation that many pediatricians still hold onto stresses the bare minimums of when to turn a child forward-facing. Who wants the minimum for their child? It’s best practice to rear-face to the limits of the child’s convertible carseat: check the label for the rear-facing weight limit and make sure there’s at least 1″ of carseat above the top of his head.
The American Academy of Pediatrics (AAP) has recommended since 2002 that after age 1 and 20 lbs., children should ride in a rear-facing convertible seat until reaching the weight limit of that carseat. They’ve just amended that policy (3/2011) to recommend rear-facing to age 2 or until they reach the “highest weight or height allowed” by that convertible carseat. (http://www.medpagetoday.com/Pediatrics/GeneralPediatrics/25435)