I've just bought a britax evolva 2-3 from mothercare as my 2.5 year old dd has out grown her seat that is ment to go up to 4 years. I wondered what age this new seat will fit her untill. She's very tall for her age but I want her to have the back rest for as long as possible as it's a lot safer and she falls asleep in the car all the time. Has anyone recently outgrown this seat? and if so how long did you use the back rest for?