Child car seat question

I live in Southern California and my son is 2 1/2 years old. I’ve been looking online for the guidelines on when they can go from child rear seating to forward seating but everyone is telling me my son should stay rear seating until he’s 4. The thing is my son went for a check up and he’s pretty tall and heavy. He weighs 40 pounds and is about 40 inches tall. He’s a big 2 1/2 year old, doctor said he was overweight. I’ve noticed his feet bend a lot with him seating rear facing and it bothers his from time to time. I feel like he should be facing forward now but I just want him to be safe and everyone says that rear facing is waaaaay safer anyone have a similar issue??