My son Collin has an old Arrow Cadet Kart. He is 4’6" and weights 75 lbs. This is his first year and instead of having him go to races we go to whatever track has open practice as often as possible. He’s made great progress this year and his lap times have dropped dramatically. He’s going to run Rookie Yamaha next season.
Our local group president thinks he needs to move up to a sportsman kart and just happens to have one he is willing to trade. It’s an older Kosmic kart.
I was going to wait until his seating position was an issue and we still have another mount hole on the chassis to move the seat further back, and while he’s not event the least overweight he’s he is pushing 80 lbs.