I had read online that this carseat goes up to 65 lbs and 52 inches with the 5-point harness, and 100 lbs and 57 inches booster. My ds is 4.5 years old, 43 lbs and 45 inches tall. We tried the booster at BRU and it only looked like he had 1-maybe 2 inches of grow room below the highest strap slot. Does he just have a super long torso or are the numbers wrong? I don't want to buy a new seat if he's just going to be back in a booster in a short preiod of time....