Could Connor Mantz win gold at worlds in the 20k race walk??

Conner would probably need to train as a walker for at least one year to have a chance.

It would almost certainly take a lot more than that, which your wording indicates you know. Race walking is really weird. There is a transition zone that for most adults is between 15 minute miles and 10 minute miles that is very awkward and inefficient. Competitive racewalkers are very far into the inefficient zone.