Rear view until 2
The AAP recently adopted the 'rear view until 2' standard for carseats.
State laws may be more lax. I encourage families to strive for optimal not acceptable safety standards. Studies show the longer a child rides rearward, the better the chance of survival in a crash. In my mind, 2 years is a minimum standard, 4 would be better, although finding a rear-facing seat for older kids is a challenge.