B.W.
We have the FirstYears TrueFit and my 3.5yr old daughter is 37" tall and 29lbs and she's able to easily rear face in it. Its a great car seat and one of the tallest on the market. In fact my 47" tall 5.5yr old is able to use the seat forward facing with room to grow. Another option for a tall kid is the AirProtect.
a rear facing car seat is outgrown when the child reaches the rear facing weight limits or the child has less than 1" of hard shell above the head. Unless one of these has been reaches the child is not too tall to rear facing. When rear facing the harness should be just at or below the shoulders.
Both my boys were 33-4" tall at a year old. They were big boys! Both slowed down considerably on the growth and are both average heights now at 8 and 5.
Anyway, the TrueFit is a great seat, with an antirebound bar for rear facing which is great! It will rear face to 35lbs and forward face to 65lbs, and fits most kids rear facing to age 3/4, and forward facing to age 6/7.