Hello Sarah!
Thanks for reaching out and leaving a review! The rating for the seat is more so by weight rather than age. Accordning to Thule it has a limit of 40 pounds and rated for 9months to 6 years old. Please note, the Aventon rear rack for the Sinch 2 model has a 55 pound weight limit.
We hope this informaiton helps! Let u sknow if you have any other questions!
Thank you,
Aventon