This might sound like a bit of a daft question however.. Ok I've got the Graco coast car seat for my little girl for when she moves up to that group of car seats 😕 however the age of it is from roughly 9months and the weight is roughly 20pounds well Arianna is 18lb at 6months. Would you wait until 9months or start putting her in from the weight. She's very long so the cat seat I got as part of my pram her legs hang over and her heads at the top.. X