My neighbor keeps her great-nephew all the time. He is 3 weeks older than Max so he is 20 months right now. Well, she was over a bit ago and asked me if her great-nephew was old enough to be in a booster. I picked my jaw up off the floor and told her absolutely not. She said she didn't think so, but that her sister (the boy's grandma, who he lives with) had bought him a booster and been using it. Her sister told her he really liked it.