I have a tall 5 year old and he is too wide in the shoulders for this seat. The head piece can he adjusted and made taller but the wings for side protection around the shoulders are not adjustable. He is 5 and 1/2 years old and he is 48.5in tall and his shoulders measure 13in wide. He is totally squeezed into this seat. I am keeping it only as a back up booster for other smaller children when we carpool, but for my son, the Diono Monterrey booster is a much better fit. Plus the shoulder wings are adjustable so hopefully he will have room to grow.