A driver should schedule the final road test to get a license once he feels comfortable enough behind the wheel to pass the test and navigate traffic safely. Different states have varying time frames to keep a learner's license for this reason.
In many states, it's possible to get a learner's driving permit at 15 years old, while the full driver's license is allowed at 16. Some states require a driver to have practiced behind the wheel for a set amount of hours, with some of those hours occurring at night. If the person feels ready to take the driving test and knows the basic rules of the road, he should call the local DMV and schedule a driving test.