Children shouldn't drive a tractor until they're 14 or 15 because they lack certain abilities that come only with maturity such as the ability to visualize and understand their surrounding environment. Experienced drivers constantly scan their surroundings, looking for things that could become hazardous. There's strong evidence in laboratory studies that children do this terribly, according to David Schwebel, a psychology professor at the University of Alabama [at Birmingham] who has worked with the National Children's Center for Rural and Agricultural Health and Safety.