Perhaps young drivers take undue risk on the roads. It makes good sense that adolescents take up demanding and challenging interests to test out their skills and their love of action and their level of responsibility before they jump headlong into driving a car or road bike on the highway.
It must be counterproductive to protect kids from all risk and for them to have none other than a super comfortable existence, at least in our society, competitive as it is.
As for small children there are responsibilities that small children can start to take up and have time enough to develope imagination and good things long before they engage in big kids stuff. As well, road and off-road safety surely relies on a little maturity.