How old is too old for kids to ride in a shopping cart?

What part of the cart? If you're talking about the little seat in the front, there's no way a nine year old would fit. And it would probably be beneath their dignity to try. lol

I could see a nine year old wanting to ride in the big basket part, but many parents wouldn't allow that, as carts usually come with a warning not to do it. A nine year old might want to stand on the back of the cart with their feet on the rack beneath the basket. You can hold on to the back of the cart and ride around backward while a parent pushes.

My grocery store people will stop people and ask them to unload older children while the clerk securely holds the cart. They would rather have a minor altercation with the customer than have an accident due to a cart tipping over with a kid climbing around on the cart. If a parent has a child in a cart, they should never turn loose of the cart, but maintain firm control at all times. Children with protective parents, already know not to climb around on the cart. It seems there are families where their children are mere household donkeys to them until they get hurt, then they become precious.

A small nine year old girl could fit into a shopping cart, but kids usually stop around 6-7. It all depends on the girls personality, if she acts more like a child this would be perfectly normal.

My nine year old niece asks to sit in the cart all the time, but she has to sit in the big basket part, but I usually tell her it's not a good idea...

About 2. No kid of 9 could fit.

Maybe 5, depends on if I can lift them.

I am still allowed and I am forty six

NO!