I think it has to do with Height and Weight rather than age
9
it usually depends on the height and weight, but you place them in an approved seat at age 5.
When you have reached adult age which in Ontario is 18.
You must place a child in an integrated child seat if the child is 3 years of age or younger.
you have to be 12
A child should transition from a car seat to a booster seat around the age of 8 or when they reach the height and weight requirements specified by the car seat manufacturer.
The age in which a child can stop using a car seat or booster seat varies from state to state. In Michigan, the child safety seat law says that a child under the age of eight years old must be in a safety seat unless they are taller than 4' 9.
at the age of 12 at the age of 12
18
4 The answer is NOT based on age but on the height and weight of your child. If your child is over 40lbs he/she can transition to a booster seat with lap/ shoulder restraint.
A child should transition from a car seat to a booster seat when they reach the age of around 8-12 years old, or when they outgrow the weight or height limits of their car seat.