Most car seats I remember were based on age height and weight. Been a while though my "baby" is 16 and driving now. If you son rides in the back there may be some models that work well with just a lap belt to hold the seat in place. If you use a booster I would recommend using lap and shoulder belts. You could do that in front or rear seat, but everything I remember recommends children never ride in the front seat. Take him cruzing, but do it as safe as you can.