I love the britax frontier 85. And im a math person. so the height an weight max on it is 5' 5" and 120 lbs. looking at a growth chart the average girl would be able to ride in it till between 17 and 18. is there anyway to justify that. or should you let you child out of the booster before that. everyone claims they want to keep the child in a booster or rf or in a 5 point as long as posiable. but when is enough enough. I was one of those people but after looking at this...