Unfortunately our son fits with 7 months just under the size (total length and width of your shoulders). He is rather small to normal size (68 cm and 7.5 kg). In addition, for a long time the shoulder girdle is much too low. From a size of about 60 cm, it is no longer correctly adjusted! This is particularly bad because the next size car seats should be used until the child can sit all right alone. So angry in retrospect very pleased to have bought this seat.
Have now bought us for the transition period to a proper child seat a Roman-carrycot. That's in the back length about 2 cm longer and extends to our little sit well.