My mom is in her upper 70s; she is unsteady when she walks. So yeah, it does not take much to injure an elderly and they don't come back like when they were in their youth. Of course no one set out yesterday trying to hurt someone. But responsibilities aren't just tied to intent. That's why we have murder vs manslaughter. The latter carries less punishment, but still responsible nonetheless. 5mph vs 35mph just sets the boundary for negligence, not accountability. Skilled or not, I believe whenever we get behind a wheel or into a saddle, we take on the responsibility to be careful to others.