So ds is 7.5 and 65lbs, my understanding is they can be out of a booster at either 80lbs or 8 years old. I can understand the weight reasoning but why the age? Can he stay in a booster over eight? Is it safer? He's 52" tall currently and it'll be a while before he's 80lbs but he's a little over 6 months from hitting the 8 year old mark and I'm wondering why then he's suddenly ok to be just in the seat?