That would be a better question for the track that you would be taking him to.
Tracks are divided on what classes and engine combos to offer. Some tracks will allow kids at 6 to start, while others insist they must be 7 or 8 before running jr 1 classes.
There is a kid kart (specific for 4-8 year olds) that is a shorter wheel base kart and uses the Comer or JRLO206 engine for power. You might check to see if your track offers that as well.
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